[automerger skipped] Add synchronized lock for ringback playing start/stop...

[automerger skipped] Add synchronized lock for ringback playing start/stop request to avoid am: 7b6c9ba0 am: 1df509d3 -s ours

am skip reason: Merged-In I143081557957f961a58fd3c1e0518f6a4af738d9 with SHA-1 7b6c9ba0 is already in history

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/services/Telecomm/+/22304956



Change-Id: Iff553f86000edf8955ee929056fad91d2a15d65a
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>