Merge "TelephonyConnection: Serialize onHold()/onUnhold()" into udc-qpr-dev am: f74ecc88ee am: a891b5db5f

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/services/Telephony/+/23215746

Change-Id: I0d8b25212e01f0de2ce50495dd4b2679f011e74d
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>