flutter#30754: [Material] Fix showDialog crasher caused by old contexts

flutter#30525: Fix cursor outside of input width

flutter#30805: Update ExpansionPanelList Samples with Scaffold Template

flutter#30537: Embedded images and added variations to ListTile sample code

flutter#30455: Prevent vertical scroll in shrine by ensuring card size fits the screen

flutter#29413: Fix MaterialApp’s _navigatorObserver when only builder used

Desktop Changes

Flutter has been making progress on expanding support for desktop-class input mechanisms with keyboard mappings, text selection, mouse wheels and hover along with the beginnings of desktop support in our tooling.

flutter#29993: Adds the keyboard mapping for Linux