Added M3 demo app (#1189)

* Added M3 demo app

* Changed to use the centralized lint configuration.

* Moved the app at the root level

* Added to CI

* Added app to beta CI and commented app on stable CI file

* Update README.md

* Addressed comments

* fixed comments

* Reverted app name in CI files.

* Added project to the Pub Dependabot config

* Linting pass for current beta channel standards

Co-authored-by: Qun Cheng <quncheng@google.com>
Co-authored-by: Craig Labenz <craig.labenz@gmail.com>

material_3_demo/lib/typography_screen.dart

@@ -0,0 +1,59 @@
+import 'package:flutter/material.dart';
+
+class TypographyScreen extends StatelessWidget {
+  const TypographyScreen({Key? key}) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    final textTheme = Theme.of(context)
+        .textTheme
+        .apply(displayColor: Theme.of(context).colorScheme.onSurface);
+    return Expanded(
+      child: ListView(
+        children: <Widget>[
+          const SizedBox(height: 7),
+          TextStyleExample(
+              name: "Display Large", style: textTheme.displayLarge!),
+          TextStyleExample(
+              name: "Display Medium", style: textTheme.displayMedium!),
+          TextStyleExample(
+              name: "Display Small", style: textTheme.displaySmall!),
+          TextStyleExample(
+              name: "Headline Large", style: textTheme.headlineLarge!),
+          TextStyleExample(
+              name: "Headline Medium", style: textTheme.headlineMedium!),
+          TextStyleExample(
+              name: "Headline Small", style: textTheme.headlineSmall!),
+          TextStyleExample(name: "Title Large", style: textTheme.titleLarge!),
+          TextStyleExample(name: "Title Medium", style: textTheme.titleMedium!),
+          TextStyleExample(name: "Title Small", style: textTheme.titleSmall!),
+          TextStyleExample(name: "Label Large", style: textTheme.labelLarge!),
+          TextStyleExample(name: "Label Medium", style: textTheme.labelMedium!),
+          TextStyleExample(name: "Label Small", style: textTheme.labelSmall!),
+          TextStyleExample(name: "Body Large", style: textTheme.bodyLarge!),
+          TextStyleExample(name: "Body Medium", style: textTheme.bodyMedium!),
+          TextStyleExample(name: "Body Small", style: textTheme.bodySmall!),
+        ],
+      ),
+    );
+  }
+}
+
+class TextStyleExample extends StatelessWidget {
+  const TextStyleExample({
+    Key? key,
+    required this.name,
+    required this.style,
+  }) : super(key: key);
+
+  final String name;
+  final TextStyle style;
+
+  @override
+  Widget build(BuildContext context) {
+    return Padding(
+      padding: const EdgeInsets.all(8.0),
+      child: Text(name, style: style),
+    );
+  }
+}