Use EdgeInsetsGeometry instead of EdgeInsets (#40775)

packages/flutter/lib/src/painting/shape_decoration.dart

@@ -178,7 +178,7 @@ class ShapeDecoration extends Decoration {
   ///
   /// This value may be misleading. See the discussion at [ShapeBorder.dimensions].
   @override
-  EdgeInsets get padding => shape.dimensions;
+  EdgeInsetsGeometry get padding => shape.dimensions;
 
   @override
   bool get isComplex => shadows != null;

packages/flutter/test/widgets/shape_decoration_test.dart

@@ -61,6 +61,14 @@ Future<void> main() async {
     );
   }, skip: isBrowser);
 
+  test('ShapeDecoration with BorderDirectional', () {
+    const ShapeDecoration decoration = ShapeDecoration(
+      shape: BorderDirectional(start: BorderSide(color: Colors.red, width: 3)),
+    );
+
+    expect(decoration.padding, isInstanceOf<EdgeInsetsDirectional>());
+  });
+
   testWidgets('TestBorder and Directionality - 1', (WidgetTester tester) async {
     final List<String> log = <String>[];
     await tester.pumpWidget(