Add an opt-out property for camera compat freeform treatment.

The name has been chosen to be future-proof for other windowing
modes and platforms.

Flag: com.android.window.flags.enable_camera_compat_for_desktop_windowing_opt_out
Test: atest WmTests:AppCompatCameraOverridesTest
Fixes: 328616176
Change-Id: I2c7e9cfde4ba139e46c070d2cbc08e853416ef0e