Added deprecation notice on switching between material2 and material3

Author: Lance Johnstone

example/lib/platform_page.dart.dart

@@ -36,22 +36,7 @@ class PlatformPage extends StatelessWidget {
                         : p.changeToMaterialPlatform();
                   }),
             ),
-            if (isMaterial(context))
-              Padding(
-                padding: const EdgeInsets.all(8.0),
-                child: PlatformElevatedButton(
-                    child: PlatformText(
-                        'Change to Material${Theme.of(context).useMaterial3 ? "" : " 3"}'),
-                    onPressed: () {
-                      final isMaterial3 = Theme.of(context).useMaterial3;
 
-                      isMaterial3
-                          ? PlatformTheme.of(context)?.changeToMaterial2(
-                              applyToBothDarkAndLightTheme: true)
-                          : PlatformTheme.of(context)?.changeToMaterial3(
-                              applyToBothDarkAndLightTheme: true);
-                    }),
-              ),
             Padding(
               padding: const EdgeInsets.all(8.0),
               child: PlatformElevatedButton(

lib/src/platform_theme.dart

@@ -102,19 +102,20 @@ class _PlatformThemeState extends State<PlatformTheme>
         : themeMode == ThemeMode.dark;
   }
 
+  @Deprecated(
+      'Switching to and from Material 2 and 3 is deprecated has no effect and wil be removed in the future.')
   void changeToMaterial3({bool applyToBothDarkAndLightTheme = false}) =>
       _setMaterialThemeType(
-          useMaterial3: true,
           applyToBothDarkAndLightTheme: applyToBothDarkAndLightTheme);
 
+  @Deprecated(
+      'Switching to and from Material 2 and 3 is deprecated has no effect and wil be removed in the future.')
   void changeToMaterial2({bool applyToBothDarkAndLightTheme = false}) =>
       _setMaterialThemeType(
-          useMaterial3: false,
           applyToBothDarkAndLightTheme: applyToBothDarkAndLightTheme);
 
   void resetMaterial({bool applyToBothDarkAndLightTheme = false}) {
     _setMaterialThemeType(
-        useMaterial3: null,
         applyToBothDarkAndLightTheme: applyToBothDarkAndLightTheme);
   }
 
@@ -123,7 +124,6 @@ class _PlatformThemeState extends State<PlatformTheme>
       false;
 
   void _setMaterialThemeType({
-    required bool? useMaterial3,
     bool applyToBothDarkAndLightTheme = false,
   }) {
     setState(() {
@@ -179,14 +179,20 @@ class PlatformThemeState {
   ThemeData? get materialLightTheme => _parent._materialLightTheme;
   ThemeData? get materialDarkTheme => _parent._materialDarkTheme;
 
+  @Deprecated(
+      'Switching to and from Material 2 and 3 is deprecated has no effect and wil be removed in the future.')
   void changeToMaterial3({bool applyToBothDarkAndLightTheme = false}) =>
       _parent.changeToMaterial3(
           applyToBothDarkAndLightTheme: applyToBothDarkAndLightTheme);
 
+  @Deprecated(
+      'Switching to and from Material 2 and 3 is deprecated has no effect and wil be removed in the future.')
   void changeToMaterial2({bool applyToBothDarkAndLightTheme = false}) =>
       _parent.changeToMaterial2(
           applyToBothDarkAndLightTheme: applyToBothDarkAndLightTheme);
 
+  @Deprecated(
+      'Switching to and from Material 2 and 3 is deprecated has no effect and wil be removed in the future.')
   void resetToMaterialDefaultVersion(
           {bool applyToBothDarkAndLightTheme = false}) =>
       _parent.resetMaterial(