Public Audio playback capture must have a valid projection

For privacy, require the app wanting to capture other app audio to have
a valid MediaProjection.

Test: adb shell audiorecorder --target /data/file.raw
Bug: 111453086

Change-Id: Ia9343b2125aea2d9c0fc5a37b6ded9237d1d0f28
Signed-off-by: Kevin Rocard <krocard@google.com>