Add flag to gate MediaSession-less output switcher

Bug: 284227163
Test: host test from setting ui.
 atest MediaOutputPreferenceControllerTest
 atest AudioOutputSwitchPreferenceControllerTest
 atest MediaOutputIndicatorSliceTest

Change-Id: I6c2378bf929b82a5c407e6b67ac8003aea22b54e
Signed-off-by: Jasmine Cha <chajasmine@google.com>
1 file changed