Added EdgeInsetsDirectional.copyWith (#137559)

Added `EdgeInsetsDirectional.copyWith` named constructor.

Fixes #137475

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

@@ -904,6 +904,22 @@ class EdgeInsetsDirectional extends EdgeInsetsGeometry {
         return EdgeInsets.fromLTRB(start, top, end, bottom);
     }
   }
+
+  /// Creates a copy of this EdgeInsetsDirectional but with the given
+  /// fields replaced with the new values.
+  EdgeInsetsDirectional copyWith({
+    double? start,
+    double? top,
+    double? end,
+    double? bottom,
+  }) {
+    return EdgeInsetsDirectional.only(
+      start: start ?? this.start,
+      top: top ?? this.top,
+      end: end ?? this.end,
+      bottom: bottom ?? this.bottom,
+    );
+  }
 }
 
 class _MixedEdgeInsets extends EdgeInsetsGeometry {

packages/flutter/test/painting/edge_insets_test.dart

@@ -279,4 +279,10 @@ void main() {
     expect(const EdgeInsetsDirectional.only(top: 4.0).add(const EdgeInsets.only(right: 3.0)).toString(), 'EdgeInsets(0.0, 4.0, 3.0, 0.0)');
     expect(const EdgeInsetsDirectional.only(start: 4.0).add(const EdgeInsets.only(left: 3.0)).toString(), 'EdgeInsets(3.0, 0.0, 0.0, 0.0) + EdgeInsetsDirectional(4.0, 0.0, 0.0, 0.0)');
   });
+
+  test('EdgeInsetsDirectional copyWith', () {
+    const EdgeInsetsDirectional sourceEdgeInsets = EdgeInsetsDirectional.only(start: 1.0, top: 2.0, bottom: 3.0, end: 4.0);
+    final EdgeInsetsDirectional copy = sourceEdgeInsets.copyWith(start: 5.0, top: 6.0);
+    expect(copy, const EdgeInsetsDirectional.only(start: 5.0, top: 6.0, bottom: 3.0, end: 4.0));
+  });
 }