[infra_ui][keyboard] Add keyboard demo entrance

app_flowy/packages/flowy_infra_ui/example/lib/home/demo_item.dart

@@ -5,7 +5,7 @@ abstract class ListItem {}
 abstract class DemoItem extends ListItem {
   String buildTitle();
 
-  void handleTap();
+  void handleTap(BuildContext context);
 }
 
 class SectionHeaderItem extends ListItem {

app_flowy/packages/flowy_infra_ui/example/lib/home/home_screen.dart

@@ -1,11 +1,13 @@
-import 'package:example/home/demo_item.dart';
+import 'package:example/keyboard/keyboard_screen.dart';
 import 'package:flutter/material.dart';
+import 'demo_item.dart';
 
 class HomeScreen extends StatelessWidget {
   const HomeScreen({Key? key}) : super(key: key);
 
   static List<ListItem> items = [
     SectionHeaderItem('Widget Demos'),
+    KeyboardItem(),
   ];
 
   @override
@@ -30,7 +32,7 @@ class HomeScreen extends StatelessWidget {
           } else if (item is DemoItem) {
             return ListTile(
               title: Text(item.buildTitle()),
-              onTap: item.handleTap,
+              onTap: () => item.handleTap(context),
             );
           }
           return const ListTile(

app_flowy/packages/flowy_infra_ui/example/lib/keyboard/keyboard_screen.dart

@@ -0,0 +1,57 @@
+import 'package:flutter/material.dart';
+import '../home/demo_item.dart';
+
+class KeyboardItem extends DemoItem {
+  @override
+  String buildTitle() => 'Keyboard Listener';
+
+  @override
+  void handleTap(BuildContext context) {
+    Navigator.of(context).push(
+      MaterialPageRoute(
+        builder: (context) {
+          return const KeyboardScreen();
+        },
+      ),
+    );
+  }
+}
+
+class KeyboardScreen extends StatefulWidget {
+  const KeyboardScreen({Key? key}) : super(key: key);
+
+  @override
+  _KeyboardScreenState createState() => _KeyboardScreenState();
+}
+
+class _KeyboardScreenState extends State<KeyboardScreen> {
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(
+        title: const Text('Keyboard Visibility Demo'),
+      ),
+      body: GestureDetector(
+        onTap: () => _dismissKeyboard(context),
+        behavior: HitTestBehavior.translucent,
+        child: Padding(
+          padding: const EdgeInsets.symmetric(horizontal: 36),
+          child: Center(
+            child: TextField(
+              style: const TextStyle(fontSize: 20),
+              controller: TextEditingController(text: 'Test'),
+            ),
+          ),
+        ),
+      ),
+    );
+  }
+
+  void _dismissKeyboard(BuildContext context) {
+    final currentFocus = FocusScope.of(context);
+
+    if (!currentFocus.hasPrimaryFocus && currentFocus.hasFocus) {
+      FocusManager.instance.primaryFocus?.unfocus();
+    }
+  }
+}