Coarse locations: Add logging to LocationFudger and LocationManagerService

We reuse the logger already present in the framework, e.g., in frameworks/base/services/core/java/com/android/server/biometrics/log/BiometricFrameworkStatsLogger.java or frameworks/base/services/core/java/com/android/server/vibrator/VibratorFrameworkStatsLogger.java.

We add three logs:
- When the population density provider is instantiated (happens once every reboot).
- When the LocationFudger contacts the Population Density provider (happens at most once per S2 cell, until the device moves to a new cell).
- When the new algorithm is used. To avoid incurring a performance hit on each query to the LocationFudger, the call to this logger is rate-limited to once every 10min max.

The log messages definitions are in https://android-review.git.corp.google.com/c/platform/frameworks/proto_logging/+/3430986

Nit: The method fetchDefaultCoarseningLevel() is renamed to better capture what it now does.

Change-Id: I9b886c0e0307dfb511812be72b3454661c0a0255

Tests:
- atest FrameworksMockingServicesTests:LocationFudgerTest
- atest FrameworksMockingServicesTests:LocationFudgerCacheTest

Test: existing tests still pass. Added a test for the rate-limiting.
Flag: android.location.flags.density_based_coarse_locations
Bug: 385288747
Change-Id: Id9402a754dd8693c1255c65001927f9a576f76b4