Add task menu item to move task to Desktop

- Call SystemUiProxy.moveToDesktop to move existing Overview tasks to desktop
- Animation polish will be handled separately
- Refactored AbstractFloatingView method into a helper to allow testing

Fix: 320310347
Test: DesktopSystemShortcutTest, AbstractFloatingViewHelperTest
Flag: ACONFIG com.android.window.flags.enable_desktop_windowing_mode DEVELOPMENT
Change-Id: I2e4e04182e46ba4750e0683ee1789ba8fada06ea