Add optional splashColor property to ExpansionTile (#172224)

This PR adds support for customizing the `splashColor` in the
`ExpansionTile` widget.

Currently, ExpansionTile uses the theme’s default splash color without
allowing overrides.
This change introduces a new optional splashColor parameter so
developers can better control the ripple effect color when the tile is
tapped.

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we expect every widget to implement].
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above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

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---------

Co-authored-by: Victor Sanni <victorsanniay@gmail.com>

Author: Musaddiq625

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

@@ -137,6 +137,7 @@ class ExpansionTile extends StatefulWidget {
     this.controlAffinity,
     this.controller,
     this.dense,
+    this.splashColor,
     this.visualDensity,
     this.minTileHeight,
     this.enableFeedback = true,
@@ -402,6 +403,25 @@ class ExpansionTile extends StatefulWidget {
   /// {@macro flutter.material.ListTile.dense}
   final bool? dense;
 
+  /// The splash color of the ink response when the tile is tapped.
+  ///
+  /// This color is passed directly to the underlying [ListTile]'s
+  /// `splashColor` property, which controls the ink ripple (splash)
+  /// animation when the tile is tapped. Internally, [ListTile] uses
+  /// an [InkWell] (which handles the actual splash effect), and so the
+  /// provided color will apply to that ripple.
+  ///
+  /// If null, the splash color will default to the current theme’s
+  /// `ThemeData.splashColor`.
+  ///
+  /// See also:
+  ///
+  /// * [ListTile.splashColor], which sets the ink splash for the tile.
+  /// * [InkWell.splashColor], which determines the color of the ripple
+  ///   effect in Material widgets.
+  /// * [ThemeData.splashColor], which provides a fallback color.
+  final Color? splashColor;
+
   /// Defines how compact the expansion tile's layout will be.
   ///
   /// {@macro flutter.material.themedata.visualDensity}
@@ -593,6 +613,7 @@ class _ExpansionTileState extends State<ExpansionTile> {
           enabled: widget.enabled,
           onTap: _tileController.isExpanded ? _tileController.collapse : _tileController.expand,
           dense: widget.dense,
+          splashColor: widget.splashColor,
           visualDensity: widget.visualDensity,
           enableFeedback: widget.enableFeedback,
           contentPadding: widget.tilePadding ?? _expansionTileTheme.tilePadding,

packages/flutter/test/material/expansion_tile_test.dart

@@ -1600,13 +1600,14 @@ void main() {
     expect(controller2, isNull);
   });
 
-  testWidgets('Check if dense, enableFeedback, visualDensity parameter is working', (
+  testWidgets('Check if dense, splashColor, enableFeedback, visualDensity parameter is working', (
     WidgetTester tester,
   ) async {
     final GlobalKey titleKey = GlobalKey();
     final GlobalKey nonDescendantKey = GlobalKey();
 
     const bool dense = true;
+    const Color splashColor = Colors.blue;
     const bool enableFeedback = false;
     const VisualDensity visualDensity = VisualDensity.compact;
 
@@ -1617,6 +1618,7 @@ void main() {
             children: <Widget>[
               ExpansionTile(
                 dense: dense,
+                splashColor: splashColor,
                 enableFeedback: enableFeedback,
                 visualDensity: visualDensity,
                 title: Text('Title', key: titleKey),
@@ -1632,6 +1634,7 @@ void main() {
     final Finder tileFinder = find.byType(ListTile);
     final ListTile tileWidget = tester.widget<ListTile>(tileFinder);
     expect(tileWidget.dense, dense);
+    expect(tileWidget.splashColor, splashColor);
     expect(tileWidget.enableFeedback, enableFeedback);
     expect(tileWidget.visualDensity, visualDensity);
   });