feat: optimize editing experience on mobile (#592)

* feat: optimize mobile editing

* feat: refactot the mobile toolbar

* feat: don't reattch text input if the selection doesn't change

* chore: update mobile toolbar layout

example/lib/home_page.dart

@@ -87,13 +87,14 @@ class _HomePageState extends State<HomePage> {
       key: _scaffoldKey,
       extendBodyBehindAppBar: PlatformExtension.isDesktopOrWeb,
       drawer: _buildDrawer(context),
+      resizeToAvoidBottomInset: false,
       appBar: AppBar(
         backgroundColor: const Color.fromARGB(255, 134, 46, 247),
         foregroundColor: Colors.white,
         surfaceTintColor: Colors.transparent,
         title: const Text('AppFlowy Editor'),
       ),
-      body: SafeArea(child: _buildBody(context)),
+      body: _buildBody(context),
     );
   }