Add new MediaProjection overlay recording mode

This overlay mode allows the MediaProjection session to only record all
layers that are z-ordered below an alert window/application overlay
rendered by the recording app.

Can only be called by select, privileged callers.

Bug: 395054309
Flag: com.android.media.projection.flags.recording_overlay
Test: atest MediaProjectionManagerServiceTest ContentRecorderTests ContentRecorderSessionTest

Change-Id: I796045464afe7d87cc1dc1e26cc800bcb188767f