Fix visual overflow for SliverMainAxisGroup (#132989)

Fixes https://github.com/flutter/flutter/issues/132788

The SliverGeometry was not set properly for SliverMainAxisGroup. Omitting hasVisualOverflow affected the Viewport's choice to apply a clip, leading to the sliver being rendered outside of the bounds of the viewport.

packages/flutter/lib/src/rendering/sliver_group.dart

@@ -288,6 +288,7 @@ class RenderSliverMainAxisGroup extends RenderSliver with ContainerRenderObjectM
       scrollExtent: totalScrollExtent,
       paintExtent: calculatePaintOffset(constraints, from: 0, to: totalScrollExtent),
       maxPaintExtent: maxPaintExtent,
+      hasVisualOverflow: totalScrollExtent > constraints.remainingPaintExtent || constraints.scrollOffset > 0.0,
     );
   }
 

packages/flutter/test/widgets/sliver_main_axis_group_test.dart

@@ -61,6 +61,7 @@ void main() {
     final RenderSliverMainAxisGroup renderGroup =
         tester.renderObject<RenderSliverMainAxisGroup>(find.byType(SliverMainAxisGroup));
     expect(renderGroup.geometry!.scrollExtent, equals(300 * 20 + 200 * 20));
+    expect(renderGroup.geometry!.hasVisualOverflow, isTrue);
   });
 
   testWidgets('SliverMainAxisGroup is laid out properly when reversed', (WidgetTester tester) async {
@@ -112,6 +113,7 @@ void main() {
     final RenderSliverMainAxisGroup renderGroup =
         tester.renderObject<RenderSliverMainAxisGroup>(find.byType(SliverMainAxisGroup));
     expect(renderGroup.geometry!.scrollExtent, equals(300 * 20 + 200 * 20));
+    expect(renderGroup.geometry!.hasVisualOverflow, isTrue);
   });
 
   testWidgets('SliverMainAxisGroup is laid out properly when horizontal', (WidgetTester tester) async {
@@ -168,6 +170,7 @@ void main() {
     final RenderSliverMainAxisGroup renderGroup =
         tester.renderObject<RenderSliverMainAxisGroup>(find.byType(SliverMainAxisGroup));
     expect(renderGroup.geometry!.scrollExtent, equals(300 * 20 + 200 * 20));
+    expect(renderGroup.geometry!.hasVisualOverflow, isTrue);
   });
 
   testWidgets('SliverMainAxisGroup is laid out properly when horizontal, reversed', (WidgetTester tester) async {
@@ -225,6 +228,7 @@ void main() {
     final RenderSliverMainAxisGroup renderGroup =
         tester.renderObject<RenderSliverMainAxisGroup>(find.byType(SliverMainAxisGroup));
     expect(renderGroup.geometry!.scrollExtent, equals(300 * 20 + 200 * 20));
+    expect(renderGroup.geometry!.hasVisualOverflow, isTrue);
   });
 
   testWidgets('Hit test works properly on various parts of SliverMainAxisGroup', (WidgetTester tester) async {