Remove prefer_const_constructors ignores (#123284)

Remove prefer_const_constructors ignores

packages/flutter/test/material/expansion_tile_test.dart

@@ -329,18 +329,17 @@ void main() {
     const Key child0Key = Key('child0');
     const Key child1Key = Key('child1');
 
-    // TODO(goderbauer): Reevaluate the following ignores when https://github.com/dart-lang/sdk/issues/51800 is fixed.
-    await tester.pumpWidget(MaterialApp( // ignore: prefer_const_constructors
-      home: Material( // ignore: prefer_const_constructors
-        child: Center( // ignore: prefer_const_constructors
-          child: ExpansionTile( // ignore: prefer_const_constructors
-            title: const Text('title'),
+    await tester.pumpWidget(const MaterialApp(
+      home: Material(
+        child: Center(
+          child: ExpansionTile(
+            title: Text('title'),
             // Set the column's alignment to Alignment.centerRight to test CrossAxisAlignment
             // of children widgets. This helps distinguish the effect of expandedAlignment
             // and expandedCrossAxisAlignment later in the test.
             expandedAlignment: Alignment.centerRight,
             expandedCrossAxisAlignment: CrossAxisAlignment.start,
-            children: const <Widget>[
+            children: <Widget>[
               SizedBox(height: 100, width: 100, key: child0Key),
               SizedBox(height: 100, width: 80, key: child1Key),
             ],

packages/flutter/test/widgets/selectable_region_context_menu_test.dart

@@ -144,16 +144,15 @@ class RenderSelectionSpy extends RenderProxyBox
 
   @override
   SelectionGeometry get value => _value;
-  // TODO(goderbauer): Reevaluate the ignore when https://github.com/dart-lang/sdk/issues/51800 is fixed.
-  SelectionGeometry _value = SelectionGeometry( // ignore: prefer_const_constructors
+  SelectionGeometry _value = const SelectionGeometry(
     hasContent: true,
     status: SelectionStatus.uncollapsed,
-    startSelectionPoint: const SelectionPoint(
+    startSelectionPoint: SelectionPoint(
       localPosition: Offset.zero,
       lineHeight: 0.0,
       handleType: TextSelectionHandleType.left,
     ),
-    endSelectionPoint: const SelectionPoint(
+    endSelectionPoint: SelectionPoint(
       localPosition: Offset.zero,
       lineHeight: 0.0,
       handleType: TextSelectionHandleType.left,

packages/flutter/test/widgets/selectable_region_test.dart

@@ -1983,16 +1983,15 @@ class RenderSelectionSpy extends RenderProxyBox
 
   @override
   SelectionGeometry get value => _value;
-  // TODO(goderbauer): Reevaluate the ignore when https://github.com/dart-lang/sdk/issues/51800 is fixed.
-  SelectionGeometry _value = SelectionGeometry( // ignore: prefer_const_constructors
+  SelectionGeometry _value = const SelectionGeometry(
     hasContent: true,
     status: SelectionStatus.uncollapsed,
-    startSelectionPoint: const SelectionPoint(
+    startSelectionPoint: SelectionPoint(
       localPosition: Offset.zero,
       lineHeight: 0.0,
       handleType: TextSelectionHandleType.left,
     ),
-    endSelectionPoint: const SelectionPoint(
+    endSelectionPoint: SelectionPoint(
       localPosition: Offset.zero,
       lineHeight: 0.0,
       handleType: TextSelectionHandleType.left,
@@ -2073,16 +2072,15 @@ class RenderSelectAll extends RenderProxyBox
 
   @override
   SelectionGeometry get value => _value;
-  // TODO(goderbauer): Reevaluate the ignore when https://github.com/dart-lang/sdk/issues/51800 is fixed.
-  SelectionGeometry _value = SelectionGeometry( // ignore: prefer_const_constructors
+  SelectionGeometry _value = const SelectionGeometry(
     hasContent: true,
     status: SelectionStatus.uncollapsed,
-    startSelectionPoint: const SelectionPoint(
+    startSelectionPoint: SelectionPoint(
       localPosition: Offset.zero,
       lineHeight: 0.0,
       handleType: TextSelectionHandleType.left,
     ),
-    endSelectionPoint: const SelectionPoint(
+    endSelectionPoint: SelectionPoint(
       localPosition: Offset.zero,
       lineHeight: 0.0,
       handleType: TextSelectionHandleType.left,