Fix `shape` and `collapsedShape` isn't applied to `ExpansionTile`'s splash ink (#141777)

This updates the previous attempt https://github.com/flutter/flutter/pull/135855 and removes the complications when testing M3 ink sparkle effect. 
Thanks to this [PR](https://github.com/flutter/flutter/pull/138757) by @Piinks 

fixes [ExpansionTile InkSplash doesn't respect Shape's borderRadius](https://github.com/flutter/flutter/issues/125779)
fixes [`ExpansionTile.backgroundColor` &  `ExpansionTile.collapsedBackgroundColor` removes splash effect](https://github.com/flutter/flutter/issues/107113)

### Code sample

<details>
<summary>expand to view the code sample</summary> 

```dart
import 'package:flutter/material.dart';

void main() => runApp(const MyApp());

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      debugShowCheckedModeBanner: false,
      home: Example(),
    );
  }
}

class Example extends StatelessWidget {
  const Example({super.key});

  @override
  Widget build(BuildContext context) {
    return const Scaffold(
      body: Center(
          child: Padding(
        padding: EdgeInsets.symmetric(horizontal: 24.0),
        child: ExpansionTile(
          collapsedBackgroundColor: Color(0x25ff0000),
          backgroundColor: Color(0x250000ff),
          collapsedShape: RoundedRectangleBorder(
            borderRadius: BorderRadius.all(Radius.circular(30.0)),
            side: BorderSide(color: Colors.black, width: 2.0),
          ),
          shape: RoundedRectangleBorder(
            borderRadius: BorderRadius.all(Radius.circular(30.0)),
            side: BorderSide(color: Colors.black, width: 2.0),
          ),
          clipBehavior: Clip.hardEdge,
          title: Text('Expansion Tile'),
          children: <Widget>[
            FlutterLogo(size: 50),
            FlutterLogo(size: 50),
            FlutterLogo(size: 50),
            FlutterLogo(size: 50),

          ],
        ),
      )),
    );
  }
}
```

</details>

### Before

<img width="789" alt="Screenshot 2024-01-18 at 18 16 15" src="https://github.com/flutter/flutter/assets/48603081/8c6a6f1e-6986-4acf-8dec-e223a682c0d7">

<img width="789" alt="Screenshot 2024-01-18 at 18 16 44" src="https://github.com/flutter/flutter/assets/48603081/f55f6a26-2128-48a1-b24d-3c14e4f6ecdc">

### After 
<img width="789" alt="Screenshot 2024-01-18 at 18 20 27" src="https://github.com/flutter/flutter/assets/48603081/7ec8b888-7319-460d-8488-9cd44c9246a6">

<img width="789" alt="Screenshot 2024-01-18 at 18 20 53" src="https://github.com/flutter/flutter/assets/48603081/80d66d5b-7eb2-4f47-ab4d-d7f469a731fa">

packages/flutter/lib/src/material/expansion_tile.dart

@@ -475,8 +475,11 @@ class ExpansionTile extends StatefulWidget {
 
   /// {@macro flutter.material.Material.clipBehavior}
   ///
+  /// If this is not null and a custom collapsed or expanded shape is provided,
+  /// the value of [clipBehavior] will be used to clip the expansion tile.
+  ///
   /// If this property is null, the [ExpansionTileThemeData.clipBehavior] is used. If that
-  /// is also null, a [Clip.none] is used
+  /// is also null, defaults to [Clip.antiAlias].
   ///
   /// See also:
   ///
@@ -656,11 +659,12 @@ class _ExpansionTileState extends State<ExpansionTile> with SingleTickerProvider
   Widget _buildChildren(BuildContext context, Widget? child) {
     final ThemeData theme = Theme.of(context);
     final ExpansionTileThemeData expansionTileTheme = ExpansionTileTheme.of(context);
+    final Color backgroundColor = _backgroundColor.value ?? expansionTileTheme.backgroundColor ?? Colors.transparent;
     final ShapeBorder expansionTileBorder = _border.value ?? const Border(
-            top: BorderSide(color: Colors.transparent),
-            bottom: BorderSide(color: Colors.transparent),
-          );
-    final Clip clipBehavior = widget.clipBehavior ?? expansionTileTheme.clipBehavior ?? Clip.none;
+      top: BorderSide(color: Colors.transparent),
+      bottom: BorderSide(color: Colors.transparent),
+    );
+    final Clip clipBehavior = widget.clipBehavior ?? expansionTileTheme.clipBehavior ?? Clip.antiAlias;
     final MaterialLocalizations localizations = MaterialLocalizations.of(context);
     final String onTapHint = _isExpanded
       ? localizations.expansionTileExpandedTapHint
@@ -679,12 +683,13 @@ class _ExpansionTileState extends State<ExpansionTile> with SingleTickerProvider
         break;
     }
 
-    return Container(
-      clipBehavior: clipBehavior,
-      decoration: ShapeDecoration(
-        color: _backgroundColor.value ?? expansionTileTheme.backgroundColor ?? Colors.transparent,
-        shape: expansionTileBorder,
-      ),
+    final Decoration decoration = ShapeDecoration(
+      color: backgroundColor,
+      shape: expansionTileBorder,
+    );
+
+    final Widget tile = Padding(
+      padding: decoration.padding,
       child: Column(
         mainAxisSize: MainAxisSize.min,
         children: <Widget>[
@@ -720,6 +725,23 @@ class _ExpansionTileState extends State<ExpansionTile> with SingleTickerProvider
         ],
       ),
     );
+
+    final bool isShapeProvided = widget.shape != null || expansionTileTheme.shape != null
+      || widget.collapsedShape != null || expansionTileTheme.collapsedShape != null;
+
+    if (isShapeProvided) {
+      return Material(
+        clipBehavior: clipBehavior,
+        color: backgroundColor,
+        shape: expansionTileBorder,
+        child: tile,
+      );
+    }
+
+    return DecoratedBox(
+      decoration: decoration,
+      child: tile,
+    );
   }
 
   @override

packages/flutter/test/material/expansion_tile_theme_test.dart

@@ -2,6 +2,11 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// This file is run as part of a reduced test set in CI on Mac and Windows
+// machines.
+@Tags(<String>['reduced-test-set'])
+library;
+
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -42,6 +47,13 @@ class TestTextState extends State<TestText> {
 }
 
 void main() {
+  Material getMaterial(WidgetTester tester) {
+    return tester.widget<Material>(find.descendant(
+      of: find.byType(ExpansionTile),
+      matching: find.byType(Material),
+    ));
+  }
+
   test('ExpansionTileThemeData copyWith, ==, hashCode basics', () {
     expect(const ExpansionTileThemeData(), const ExpansionTileThemeData().copyWith());
     expect(const ExpansionTileThemeData().hashCode, const ExpansionTileThemeData().copyWith().hashCode);
@@ -173,21 +185,16 @@ void main() {
       ),
     );
 
-    final ShapeDecoration shapeDecoration =  tester.firstWidget<Container>(find.descendant(
-      of: find.byKey(tileKey),
-      matching: find.byType(Container),
-    )).decoration! as ShapeDecoration;
+    // When a custom shape is provided, ExpansionTile will use the
+    // Material widget to draw the shape and background color
+    // instead of a Container.
+    final Material material = getMaterial(tester);
 
-    final Clip tileClipBehavior = tester.firstWidget<Container>(find.descendant(
-      of: find.byKey(tileKey),
-      matching: find.byType(Container),
-    )).clipBehavior;
-
-    // expansionTile should have Clip.antiAlias as clipBehavior
-    expect(tileClipBehavior, clipBehavior);
+    // ExpansionTile should have Clip.antiAlias as clipBehavior.
+    expect(material.clipBehavior, clipBehavior);
 
     // Check the tile's collapsed background color when collapsedBackgroundColor is applied.
-    expect(shapeDecoration.color, collapsedBackgroundColor);
+    expect(material.color, collapsedBackgroundColor);
 
     final Rect titleRect = tester.getRect(find.text('Collapsed Tile'));
     final Rect trailingRect = tester.getRect(find.byIcon(Icons.expand_more));
@@ -211,7 +218,7 @@ void main() {
     // Check the collapsed text color when textColor is applied.
     expect(getTextColor(), collapsedTextColor);
     // Check the collapsed ShapeBorder when shape is applied.
-    expect(shapeDecoration.shape, collapsedShape);
+    expect(material.shape, collapsedShape);
   });
 
   testWidgets('ExpansionTileTheme - expanded', (WidgetTester tester) async {
@@ -232,6 +239,7 @@ void main() {
       top: BorderSide(color: Colors.green),
       bottom: BorderSide(color: Colors.green),
     );
+    const Clip clipBehavior = Clip.none;
 
     await tester.pumpWidget(
       MaterialApp(
@@ -248,6 +256,7 @@ void main() {
             collapsedTextColor: collapsedTextColor,
             shape: shape,
             collapsedShape: collapsedShape,
+            clipBehavior: clipBehavior,
           ),
         ),
         home: Material(
@@ -264,12 +273,12 @@ void main() {
       ),
     );
 
-    final ShapeDecoration shapeDecoration =  tester.firstWidget<Container>(find.descendant(
-      of: find.byKey(tileKey),
-      matching: find.byType(Container),
-    )).decoration! as ShapeDecoration;
+    // When a custom shape is provided, ExpansionTile will use the
+    // Material widget to draw the shape and background color
+    // instead of a Container.
+    final Material material = getMaterial(tester);
     // Check the tile's background color when backgroundColor is applied.
-    expect(shapeDecoration.color, backgroundColor);
+    expect(material.color, backgroundColor);
 
     final Rect titleRect = tester.getRect(find.text('Expanded Tile'));
     final Rect trailingRect = tester.getRect(find.byIcon(Icons.expand_more));
@@ -293,7 +302,9 @@ void main() {
     // Check the expanded text color when textColor is applied.
     expect(getTextColor(), textColor);
     // Check the expanded ShapeBorder when shape is applied.
-    expect(shapeDecoration.shape, shape);
+    expect(material.shape, shape);
+    // Check the clipBehavior when shape is applied.
+    expect(material.clipBehavior, clipBehavior);
 
     // Check the child position when expandedAlignment is applied.
     final Rect childRect = tester.getRect(find.text('Tile 1'));