[Dev option] Add a dev option to enable DW.

Default value of this dev options solely depends on
enable_desktop_windowing_mode, which is intended

Toggle is shown only if DW is eligible on device

Currently this option only overrides features guarded by
enable_desktop_windowing_mode, later on it will be used to override a
few other DW features

Test: Added tests. Locally tested CUJs
Bug: 348186127
Bug: 348193756
Flag: com.android.window.flags.show_desktop_windowing_dev_option

Change-Id: I1c1f946b586a5ca0440b29879925ba1a624717aa