Add indexInParent to SemanticsNode debug information (#142826)

https://github.com/flutter/flutter/issues/93232

packages/flutter/lib/src/semantics/semantics.dart

@@ -2959,6 +2959,7 @@ class SemanticsNode with DiagnosticableTreeMixin {
     properties.add(DoubleProperty('scrollExtentMin', scrollExtentMin, defaultValue: null));
     properties.add(DoubleProperty('scrollPosition', scrollPosition, defaultValue: null));
     properties.add(DoubleProperty('scrollExtentMax', scrollExtentMax, defaultValue: null));
+    properties.add(IntProperty('indexInParent', indexInParent, defaultValue: null));
     properties.add(DoubleProperty('elevation', elevation, defaultValue: 0.0));
     properties.add(DoubleProperty('thickness', thickness, defaultValue: 0.0));
   }

packages/flutter/test/semantics/semantics_test.dart

@@ -699,6 +699,7 @@ void main() {
       '   scrollExtentMin: null\n'
       '   scrollPosition: null\n'
       '   scrollExtentMax: null\n'
+      '   indexInParent: null\n'
       '   elevation: 0.0\n'
       '   thickness: 0.0\n',
     );
@@ -823,6 +824,7 @@ void main() {
       '   scrollExtentMin: null\n'
       '   scrollPosition: null\n'
       '   scrollExtentMax: null\n'
+      '   indexInParent: null\n'
       '   elevation: 0.0\n'
       '   thickness: 0.0\n',
     );
@@ -978,6 +980,10 @@ void main() {
     );
   });
 
+  test('SemanticsNode.indexInParent appears in string output', () async {
+    final SemanticsNode node = SemanticsNode()..indexInParent = 10;
+    expect(node.toString(), contains('indexInParent: 10'));
+  });
 }
 
 class TestRender extends RenderProxyBox {