Specifically:

• Fix cursor keys and delete
• modifier keys likely using https://docs.microsoft.com/en-us/uwp/api/windows.ui.core.corewindow.getkeystate?view=winrt-19041
• shortcut support
• handing unicode correctly
• handling UWP specific system keys like back
• refactor OnKey method in WindowBindingHandlerDelegate to remove need for win32 magic values in UWP implementation
• remove action code from game_pad_cursor_winuwp.cc OnGamepadButtonPressed and OnGamepadButtonRelased
• make sure that once IME support is landed, that it behaves nicely with key events