AudioService optimize camera sound forced access

Use AtomicBoolean for the "camera sound forced" boolean
instead of protecting it by mSettingsLock.

Remote sync on mSettingsLock in VolumeSteamState methods
readSettings() and setIndex() which do not call into
other methods that synchronize on this lock.

Bug: 393961222
Bug: 287066735
Flag: EXEMPT bug fix
Test: atest VolumeHelperTest ; atest CameraTest
Change-Id: Ic355307d1b5b0305fef55f2019d6db8580dd9437