Feat: TextField can scroll when disabled (#140922)

This PR is adding a flag parameter to the `TextField` widget. This flag controls whether the TextField ignores pointers. The flag takes priority over other TextField behaviors such as enabled, so it can be useful when trying to have a disabled TextField that can be scrolled (behavior observed using TextArea on the web).

Adding a flag parameter to `TextField` helps with more customization and flexibility to the widget which can improve user experience. I am open to other ideas.   

Fixes issue #140147 

Before: 

https://github.com/flutter/flutter/assets/66151079/293e5b4e-3126-4a00-824d-1530aeaa494b

After:

https://github.com/flutter/flutter/assets/66151079/08c1af09-3bf9-4b49-b684-dda4dd920503

Usage:
```dart
child: TextField(
  ignorePointer: false,
  enabled: false,
),
```

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

@@ -285,6 +285,7 @@ class TextField extends StatefulWidget {
     this.onAppPrivateCommand,
     this.inputFormatters,
     this.enabled,
+    this.ignorePointers,
     this.cursorWidth = 2.0,
     this.cursorHeight,
     this.cursorRadius,
@@ -598,6 +599,11 @@ class TextField extends StatefulWidget {
   /// [InputDecoration.enabled] property.
   final bool? enabled;
 
+  /// Determines whether this widget ignores pointer events.
+  ///
+  /// Defaults to null, and when null, does nothing.
+  final bool? ignorePointers;
+
   /// {@macro flutter.widgets.editableText.cursorWidth}
   final double cursorWidth;
 
@@ -979,7 +985,7 @@ class _TextFieldState extends State<TextField> with RestorationMixin implements
   final GlobalKey<EditableTextState> editableTextKey = GlobalKey<EditableTextState>();
 
   @override
-  bool get selectionEnabled => widget.selectionEnabled;
+  bool get selectionEnabled => widget.selectionEnabled && _isEnabled;
   // End of API for TextSelectionGestureDetectorBuilderDelegate.
 
   bool get _isEnabled =>  widget.enabled ?? widget.decoration?.enabled ?? true;
@@ -1559,7 +1565,7 @@ class _TextFieldState extends State<TextField> with RestorationMixin implements
       onExit: (PointerExitEvent event) => _handleHover(false),
       child: TextFieldTapRegion(
         child: IgnorePointer(
-          ignoring: !_isEnabled,
+          ignoring: widget.ignorePointers ?? !_isEnabled,
           child: AnimatedBuilder(
             animation: controller, // changes the _currentLength
             builder: (BuildContext context, Widget? child) {

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

@@ -142,6 +142,7 @@ class TextFormField extends FormField<String> {
     super.validator,
     List<TextInputFormatter>? inputFormatters,
     bool? enabled,
+    bool? ignorePointers,
     double cursorWidth = 2.0,
     double? cursorHeight,
     Radius? cursorRadius,
@@ -238,6 +239,7 @@ class TextFormField extends FormField<String> {
                onSubmitted: onFieldSubmitted,
                inputFormatters: inputFormatters,
                enabled: enabled ?? decoration?.enabled ?? true,
+               ignorePointers: ignorePointers,
                cursorWidth: cursorWidth,
                cursorHeight: cursorHeight,
                cursorRadius: cursorRadius,

packages/flutter/test/material/text_field_test.dart

@@ -6535,6 +6535,55 @@ void main() {
     semantics.dispose();
   });
 
+  testWidgets('Can scroll multiline input when disabled', (WidgetTester tester) async {
+    final Key textFieldKey = UniqueKey();
+    final TextEditingController controller = _textEditingController(
+      text: kMoreThanFourLines,
+    );
+
+    await tester.pumpWidget(
+      overlay(
+        child: TextField(
+          dragStartBehavior: DragStartBehavior.down,
+          key: textFieldKey,
+          controller: controller,
+          ignorePointers: false,
+          enabled: false,
+          style: const TextStyle(color: Colors.black, fontSize: 34.0),
+          maxLines: 2,
+        ),
+      ),
+    );
+
+    RenderBox findInputBox() => tester.renderObject(find.byKey(textFieldKey));
+    final RenderBox inputBox = findInputBox();
+
+    // Check that the last line of text is not displayed.
+    final Offset firstPos = textOffsetToPosition(tester, kMoreThanFourLines.indexOf('First'));
+    final Offset fourthPos = textOffsetToPosition(tester, kMoreThanFourLines.indexOf('Fourth'));
+    expect(firstPos.dx, fourthPos.dx);
+    expect(firstPos.dy, lessThan(fourthPos.dy));
+    expect(inputBox.hitTest(BoxHitTestResult(), position: inputBox.globalToLocal(firstPos)), isTrue);
+    expect(inputBox.hitTest(BoxHitTestResult(), position: inputBox.globalToLocal(fourthPos)), isFalse);
+
+    final TestGesture gesture = await tester.startGesture(firstPos, pointer: 7);
+    await tester.pump();
+    await gesture.moveBy(const Offset(0.0, -1000.0));
+    await tester.pumpAndSettle();
+    await gesture.moveBy(const Offset(0.0, -1000.0));
+    await tester.pumpAndSettle();
+    await gesture.up();
+    await tester.pumpAndSettle();
+
+    // Now the first line is scrolled up, and the fourth line is visible.
+    final Offset finalFirstPos = textOffsetToPosition(tester, kMoreThanFourLines.indexOf('First'));
+    final Offset finalFourthPos = textOffsetToPosition(tester, kMoreThanFourLines.indexOf('Fourth'));
+
+    expect(finalFirstPos.dy, lessThan(firstPos.dy));
+    expect(inputBox.hitTest(BoxHitTestResult(), position: inputBox.globalToLocal(finalFirstPos)), isFalse);
+    expect(inputBox.hitTest(BoxHitTestResult(), position: inputBox.globalToLocal(finalFourthPos)), isTrue);
+  });
+
   testWidgets('Disabled text field does not have tap action', (WidgetTester tester) async {
     final SemanticsTester semantics = SemanticsTester(tester);
     await tester.pumpWidget(