Deprecate old SnackBar methods (#67947)

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

@@ -2146,7 +2146,10 @@ class ScaffoldState extends State<Scaffold> with TickerProviderStateMixin {
   /// See also:
   ///
   ///   * [ScaffoldMessenger], this should be used instead to manage [SnackBar]s.
-  // TODO(Piinks): Deprecate & defer to ScaffoldMessenger after customers are migrated.
+  @Deprecated(
+    'Use ScaffoldMessenger.showSnackBar. '
+    'This feature was deprecated after v1.23.0-14.0.pre.'
+  )
   ScaffoldFeatureController<SnackBar, SnackBarClosedReason> showSnackBar(SnackBar snackbar) {
     _snackBarController ??= SnackBar.createAnimationController(vsync: this)
       ..addStatusListener(_handleSnackBarStatusChange);
@@ -2205,7 +2208,10 @@ class ScaffoldState extends State<Scaffold> with TickerProviderStateMixin {
   /// See also:
   ///
   ///   * [ScaffoldMessenger], this should be used instead to manage [SnackBar]s.
-  // TODO(Piinks): Deprecate & defer to ScaffoldMessenger after customers are migrated
+  @Deprecated(
+    'Use ScaffoldMessenger.removeCurrentSnackBar. '
+    'This feature was deprecated after v1.23.0-14.0.pre.'
+  )
   void removeCurrentSnackBar({ SnackBarClosedReason reason = SnackBarClosedReason.remove }) {
     assert(reason != null);
 
@@ -2247,7 +2253,10 @@ class ScaffoldState extends State<Scaffold> with TickerProviderStateMixin {
   /// See also:
   ///
   ///   * [ScaffoldMessenger], this should be used instead to manage [SnackBar]s.
-  // TODO(Piinks): Deprecate & defer to ScaffoldMessenger after customers are migrated.
+  @Deprecated(
+    'Use ScaffoldMessenger.hideCurrentSnackBar. '
+    'This feature was deprecated after v1.23.0-14.0.pre.'
+  )
   void hideCurrentSnackBar({ SnackBarClosedReason reason = SnackBarClosedReason.hide }) {
     assert(reason != null);