Fixing ExpansionTile expandedAlignment not Accepts AlignmentGeometry … (#180814)

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*the expandedAlignment defined as Alignment , not as AlignmentGeometry
even if _buildBody returns Align widget which accepts alignment property
as AlignmentGeometry.*

#180813

## I have included 2 tests in the [flutter/tests] :
1- ExpansionTile expandedAlignment with directional test
2-ExpansionTile expandedCrossAxisAlignment with directional
expandedAlignment test

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
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.

---------

Co-authored-by: Victor Sanni <victorsanniay@gmail.com>
Co-authored-by: Tong Mu <dkwingsmt@users.noreply.github.com>

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

@@ -272,7 +272,7 @@ class ExpansionTile extends StatefulWidget {
   ///
   /// * [ExpansionTileTheme.of], which returns the nearest [ExpansionTileTheme]'s
   ///   [ExpansionTileThemeData].
-  final Alignment? expandedAlignment;
+  final AlignmentGeometry? expandedAlignment;
 
   /// Specifies the alignment of each child within [children] when the tile is expanded.
   ///

packages/flutter/test/material/expansion_tile_test.dart

@@ -336,6 +336,40 @@ void main() {
     expect(columnRect.right, 100.0);
   });
 
+  testWidgets('ExpansionTile expandedAlignment with directional test', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      const MaterialApp(
+        home: Directionality(
+          textDirection: TextDirection.rtl,
+          child: Material(
+            child: Center(
+              child: ExpansionTile(
+                title: Text('title'),
+                expandedAlignment: AlignmentDirectional.topEnd,
+                children: <Widget>[
+                  SizedBox(height: 100, width: 100),
+                  SizedBox(height: 100, width: 80),
+                ],
+              ),
+            ),
+          ),
+        ),
+      ),
+    );
+
+    await tester.tap(find.text('title'));
+    await tester.pumpAndSettle();
+
+    final Rect columnRect = tester.getRect(find.byType(Column).last);
+
+    // The expandedAlignment is used to define the alignment of the Column widget in
+    // expanded tile, not the alignment of the children inside the Column.
+    expect(columnRect.left, 0.0);
+    // The width of the Column is the width of the largest child. The largest width
+    // being 100.0, the offset of the right edge of Column from X-axis should be 100.0.
+    expect(columnRect.right, 100.0);
+  });
+
   testWidgets('ExpansionTile expandedCrossAxisAlignment test', (WidgetTester tester) async {
     const child0Key = Key('child0');
     const child1Key = Key('child1');
@@ -382,6 +416,57 @@ void main() {
     expect(child1Rect.left, 700.0);
   });
 
+  testWidgets('ExpansionTile expandedCrossAxisAlignment with directional expandedAlignment test', (
+    WidgetTester tester,
+  ) async {
+    const child0Key = Key('child0');
+    const child1Key = Key('child1');
+
+    await tester.pumpWidget(
+      const MaterialApp(
+        home: Directionality(
+          textDirection: TextDirection.rtl,
+          child: Material(
+            child: Center(
+              child: ExpansionTile(
+                title: Text('title'),
+                // Set the column's alignment to AlignmentDirectional.centerStart to test CrossAxisAlignment
+                // of children widgets. This helps distinguish the effect of expandedAlignment
+                // and expandedCrossAxisAlignment later in the test.
+                expandedAlignment: AlignmentDirectional.centerStart,
+                expandedCrossAxisAlignment: CrossAxisAlignment.end,
+                children: <Widget>[
+                  SizedBox(height: 100, width: 100, key: child0Key),
+                  SizedBox(height: 100, width: 80, key: child1Key),
+                ],
+              ),
+            ),
+          ),
+        ),
+      ),
+    );
+
+    await tester.tap(find.text('title'));
+    await tester.pumpAndSettle();
+
+    final Rect columnRect = tester.getRect(find.byType(Column).last);
+    final Rect child0Rect = tester.getRect(find.byKey(child0Key));
+    final Rect child1Rect = tester.getRect(find.byKey(child1Key));
+
+    // With `textDirection` set to `TextDirection.rtl`, `AlignmentDirectional.centerStart`
+    // resolves to `Alignment.centerRight`. The column of children should be aligned to the
+    // center right of the expanded tile.
+    expect(columnRect.right, 800.0);
+    // The width of the Column is the width of the largest child. The largest width
+    // being 100.0, the offset of the left edge of Column from X-axis should be 700.0.
+    expect(columnRect.left, 700.0);
+
+    // With `textDirection` set to `TextDirection.rtl`, `CrossAxisAlignment.end` aligns children to the left.
+    // The offset of the left edge of both children from the X-axis should be 700.0.
+    expect(child0Rect.left, 700.0);
+    expect(child1Rect.left, 700.0);
+  });
+
   testWidgets('CrossAxisAlignment.baseline is not allowed', (WidgetTester tester) async {
     expect(
       () {