Not to use handler thread in GnssGeofenceProvider

- Synchronize the calls to native methods with a lock.
- When native calls come back to GnssLocationProvider, make sure to post
tasks on the background thread so the lock is released.

Bug: 116788068
Change-Id: I613c9bb7190ce19100b2bc154e3cda92bf44e2a7
Fixes: 116788068
Test: atest GnssGeofenceProviderTest