Remove deprecated Scaffold SnackBar API (#98549)

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

@@ -122,7 +122,7 @@ class _SnackBarActionState extends State<SnackBarAction> {
       _haveTriggeredAction = true;
     });
     widget.onPressed();
-    Scaffold.of(context).hideCurrentSnackBar(reason: SnackBarClosedReason.action);
+    ScaffoldMessenger.of(context).hideCurrentSnackBar(reason: SnackBarClosedReason.action);
   }
 
   @override
@@ -583,14 +583,14 @@ class _SnackBarState extends State<SnackBar> {
       container: true,
       liveRegion: true,
       onDismiss: () {
-        Scaffold.of(context).removeCurrentSnackBar(reason: SnackBarClosedReason.dismiss);
+        ScaffoldMessenger.of(context).removeCurrentSnackBar(reason: SnackBarClosedReason.dismiss);
       },
       child: Dismissible(
         key: const Key('dismissible'),
         direction: widget.dismissDirection,
         resizeDuration: null,
         onDismissed: (DismissDirection direction) {
-          Scaffold.of(context).removeCurrentSnackBar(reason: SnackBarClosedReason.swipe);
+          ScaffoldMessenger.of(context).removeCurrentSnackBar(reason: SnackBarClosedReason.swipe);
         },
         child: snackBar,
       ),

packages/flutter/test/material/debug_test.dart

@@ -263,8 +263,10 @@ void main() {
         ),
       ),
     ));
-    // The Scaffold should assert we still have an ancestor ScaffoldMessenger in
-    // order to dismiss the SnackBar from the ScaffoldMessenger.
+    // Tap SnackBarAction to dismiss.
+    // The SnackBarAction should assert we still have an ancestor
+    // ScaffoldMessenger in order to dismiss the SnackBar from the
+    // Scaffold.
     await tester.tap(find.text('Test'));
     FlutterError.onError = oldHandler;
 
@@ -286,11 +288,67 @@ void main() {
     expect(error.toStringDeep(), equalsIgnoringHashCodes(
       'FlutterError\n'
       '   No ScaffoldMessenger widget found.\n'
-      '   Scaffold widgets require a ScaffoldMessenger widget ancestor.\n'
+      '   SnackBarAction widgets require a ScaffoldMessenger widget\n'
+      '   ancestor.\n'
       '   The specific widget that could not find a ScaffoldMessenger\n'
       '   ancestor was:\n'
-      '     Scaffold-[LabeledGlobalKey<ScaffoldState>#00829]\n'
+      '     SnackBarAction\n'
       '   The ancestors of this widget were:\n'
+      '     TextButtonTheme\n'
+      '     Padding\n'
+      '     Row\n'
+      '     Padding\n'
+      '     MediaQuery\n'
+      '     Padding\n'
+      '     SafeArea\n'
+      '     FadeTransition\n'
+      '     IconTheme\n'
+      '     IconTheme\n'
+      '     _InheritedCupertinoTheme\n'
+      '     CupertinoTheme\n'
+      '     _InheritedTheme\n'
+      '     Theme\n'
+      '     DefaultTextStyle\n'
+      '     AnimatedDefaultTextStyle\n'
+      '     _InkFeatures-[GlobalKey#00000 ink renderer]\n'
+      '     NotificationListener<LayoutChangedNotification>\n'
+      '     PhysicalModel\n'
+      '     AnimatedPhysicalModel\n'
+      '     Material\n'
+      '     FractionalTranslation\n'
+      '     SlideTransition\n'
+      '     Listener\n'
+      '     _GestureSemantics\n'
+      '     RawGestureDetector\n'
+      '     GestureDetector\n'
+      "     Dismissible-[<'dismissible'>]\n"
+      '     Semantics\n'
+      '     Align\n'
+      '     AnimatedBuilder\n'
+      '     ClipRect\n'
+      '     KeyedSubtree-[GlobalKey#00000]\n'
+      '     _EffectiveTickerMode\n'
+      '     TickerMode\n'
+      '     Offstage\n'
+      '     SizedBox\n'
+      '     Hero\n'
+      '     SnackBar-[#00000]\n'
+      '     MediaQuery\n'
+      '     LayoutId-[<_ScaffoldSlot.snackBar>]\n'
+      '     CustomMultiChildLayout\n'
+      '     AnimatedBuilder\n'
+      '     DefaultTextStyle\n'
+      '     AnimatedDefaultTextStyle\n'
+      '     _InkFeatures-[GlobalKey#00000 ink renderer]\n'
+      '     NotificationListener<LayoutChangedNotification>\n'
+      '     PhysicalModel\n'
+      '     AnimatedPhysicalModel\n'
+      '     Material\n'
+      '     _ScrollMetricsNotificationObserverScope\n'
+      '     NotificationListener<ScrollMetricsNotification>\n'
+      '     ScrollMetricsNotificationObserver\n'
+      '     _ScaffoldScope\n'
+      '     Scaffold-[LabeledGlobalKey<ScaffoldState>#00000]\n'
       '     MediaQuery\n'
       '     Directionality\n'
       '     [root]\n'