Add a flag for Camera Compat.

Existing code is protected with a flag in App Compat aconfig - we should replace it with Desktop Windowing flag to make dogfooding easier.

Flag: com.android.window.flags.enable_camera_compat_for_desktop_windowing
Bug: 344567658
Test: N/A, not used yet.
Change-Id: I7bc7ced2309947d1e145cbdd52906fa9b392c4c2