Update Gallery demo app themes for Material3 compatibility (#131093)

dev/integration_tests/flutter_gallery/lib/demo/pesto_demo.dart

@@ -23,8 +23,9 @@ const double _kRecipePageMaxWidth = 500.0;
 final Set<Recipe?> _favoriteRecipes = <Recipe?>{};
 
 final ThemeData _kTheme = ThemeData(
+  appBarTheme: const AppBarTheme(foregroundColor: Colors.white, backgroundColor: Colors.teal),
   brightness: Brightness.light,
-  primarySwatch: Colors.teal,
+  floatingActionButtonTheme: const FloatingActionButtonThemeData(foregroundColor: Colors.white),
 );
 
 class PestoHome extends StatelessWidget {

dev/integration_tests/flutter_gallery/lib/demo/shrine/app.dart

@@ -92,6 +92,7 @@ ThemeData _buildShrineTheme() {
     textTheme: _buildShrineTextTheme(base.textTheme),
     primaryTextTheme: _buildShrineTextTheme(base.primaryTextTheme),
     iconTheme: _customIconTheme(base.iconTheme),
+    appBarTheme: const AppBarTheme(backgroundColor: kShrinePink100),
   );
 }
 

dev/integration_tests/flutter_gallery/lib/demo/shrine/login.dart

@@ -99,7 +99,7 @@ class _LoginPageState extends State<LoginPage> {
                     // of Shrine completely.
                     Navigator.of(context, rootNavigator: true).pop();
                   },
-                  child: const Text('CANCEL'),
+                  child: Text('CANCEL', style: Theme.of(context).textTheme.bodySmall),
                 ),
                 ElevatedButton(
                   style: ElevatedButton.styleFrom(
@@ -111,7 +111,7 @@ class _LoginPageState extends State<LoginPage> {
                   onPressed: () {
                     Navigator.pop(context);
                   },
-                  child: const Text('NEXT'),
+                  child: Text('NEXT', style: Theme.of(context).textTheme.bodySmall),
                 ),
               ],
             ),