Population Density Provider: add cache hint

Adds a parameter to indicate the desired answer size when querying the coarsened cells. This allows the framework to indicate its cache size, and the provider to answer with the right amount of cells.

Tests:
- atest CtsLocationNoneTestCases:PopulationDensityProviderBaseTest
- atest FrameworksMockingServicesTests:LocationProviderManagerTest
- atest FrameworksMockingServicesTests:LocationFudgerTest
- atest FrameworksMockingServicesTests:LocationFudgerCacheTest
Test: manual atest on Pixel 7 pro (see above)
Bug: 381286551
Flag: android.location.flags.density_based_coarse_locations

Change-Id: Ib0d26e8ce0e1164ff30b45e2d3deddb67f68a83b