(IMS Threading refactoring) Telephony IMS classes to schedule IMS callback on the main thread am: add3b8d76e am: 62a61e86a2 am: b5ccb150d6

Original change: https://android-review.googlesource.com/c/platform/frameworks/base/+/1964909

Change-Id: I28a4d11eb44dd5b0c91b129767d9596b55698497