Reduce lock contention when debugging

Uses a ReaderWriterMutex for the breakpoint lock to reduce contention during
debugging session.

Also adds missing thread safety annotations on fields and methods related to
instrumentation and debugging.

Bug: 16814665
Bug: 11667502

(cherry picked from commit 59d9d668)

Change-Id: I5f1156da8c6cc8316d6db16e6cfb2470fe289ad3