Update "Play media to" in Sound Settings

-Change string to "Play <APP Label> on"
-Hide it when there is no local playback
-Disable search index
-Add test cases

Bug: 155720628
Test: make -j50 RunSettingsRoboTests
Change-Id: Id104d5b49c069a761e4cf82385bf1225d494c95e
3 files changed