Add compat annotation processor for services/core.

We have compat annotations in services/core (specifically
NATIVE_HEAP_POINTER_TAGGING and CTS_SYSTEM_API_CHANGEID, and soon
NATIVE_MEMORY_TAGGING) so we need to add the processor.

Bug: 135754954
Bug: 135772972
Change-Id: I134c67907abdba1dee971111498c6e50da68a768
Merged-In: I25c6339c6adeb907878596332f57e2fa229bfda9