added enabled to search anchor (flutter#153256)

Added the same parameter from flutter#137388 to the `SearchAnchor`

This PR will fix: flutter#150331

Author: Macacoazul01

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

@@ -137,6 +137,7 @@ class SearchAnchor extends StatefulWidget {
     required this.suggestionsBuilder,
     this.textInputAction,
     this.keyboardType,
+    this.enabled = true,
   });
 
   /// Create a [SearchAnchor] that has a [SearchBar] which opens a search view.
@@ -350,6 +351,13 @@ class SearchAnchor extends StatefulWidget {
   /// Defaults to the default value specified in [TextField].
   final TextInputType? keyboardType;
 
+  /// Whether or not this widget is currently interactive.
+  ///
+  /// When false, the widget will ignore taps and appear dimmed.
+  ///
+  /// Defaults to true.
+  final bool enabled;
+
   @override
   State<SearchAnchor> createState() => _SearchAnchorState();
 }
@@ -450,15 +458,25 @@ class _SearchAnchorState extends State<SearchAnchor> {
     };
   }
 
+  double _getOpacity() {
+    if (widget.enabled) {
+      return _anchorIsVisible ? 1.0 : 0.0;
+    }
+    return _kDisableSearchBarOpacity;
+  }
+
   @override
   Widget build(BuildContext context) {
     return AnimatedOpacity(
       key: _anchorKey,
-      opacity: _anchorIsVisible ? 1.0 : 0.0,
+      opacity: _getOpacity(),
       duration: _kAnchorFadeDuration,
-      child: GestureDetector(
-        onTap: _openView,
-        child: widget.builder(context, _searchController),
+      child: IgnorePointer(
+        ignoring: !widget.enabled,
+        child: GestureDetector(
+          onTap: _openView,
+          child: widget.builder(context, _searchController),
+        ),
       ),
     );
   }
@@ -1317,7 +1335,11 @@ class SearchBar extends StatefulWidget {
   /// {@macro flutter.widgets.editableText.textCapitalization}
   final TextCapitalization? textCapitalization;
 
-  /// If false the text field is "disabled" so the SearchBar will ignore taps.
+  /// Whether or not this widget is currently interactive.
+  ///
+  /// When false, the widget will ignore taps and appear dimmed.
+  ///
+  /// Defaults to true.
   final bool enabled;
 
   /// {@macro flutter.widgets.editableText.autofocus}

packages/flutter/test/material/search_anchor_test.dart

@@ -3016,6 +3016,56 @@ void main() {
     expect(opacityWidget.opacity, 0.38);
   });
 
+  testWidgets('Check SearchAnchor opacity when disabled', (WidgetTester tester) async {
+    await tester.pumpWidget(MaterialApp(
+      home: Center(
+        child: Material(
+          child: SearchAnchor(
+            enabled: false,
+            builder: (BuildContext context, SearchController controller) {
+              return const Icon(Icons.search);
+            },
+            suggestionsBuilder: (BuildContext context, SearchController controller) {
+              return <Widget>[];
+            },
+          ),
+        ),
+      ),
+    ));
+
+    final Finder searchBarFinder = find.byType(SearchAnchor);
+    expect(searchBarFinder, findsOneWidget);
+    final Finder opacityFinder = find.descendant(
+      of: searchBarFinder,
+      matching: find.byType(AnimatedOpacity),
+    );
+    expect(opacityFinder, findsOneWidget);
+    final AnimatedOpacity opacityWidget = tester.widget<AnimatedOpacity>(opacityFinder);
+    expect(opacityWidget.opacity, 0.38);
+  });
+
+  testWidgets('SearchAnchor tap failed when disabled', (WidgetTester tester) async {
+    await tester.pumpWidget(MaterialApp(
+      home: Center(
+        child: Material(
+          child: SearchAnchor(
+            enabled: false,
+            builder: (BuildContext context, SearchController controller) {
+              return const Icon(Icons.search);
+            },
+            suggestionsBuilder: (BuildContext context, SearchController controller) {
+              return <Widget>[];
+            },
+          ),
+        ),
+      ),
+    ));
+
+    final Finder searchBarFinder = find.byType(SearchAnchor);
+    expect(searchBarFinder, findsOneWidget);
+    expect(searchBarFinder.hitTestable().tryEvaluate(), false);
+  });
+
   testWidgets('SearchAnchor respects headerHeight', (WidgetTester tester) async {
     await tester.pumpWidget(MaterialApp(
       home: Center(