Tidy up the "unbundled" provider API

This commit introduces a LocationTimeZoneEventUnbundled, as
LocationTimeZoneEvent will not be on another API surface so cannot be
reused. (The equivalent from LocationProvider is Location, which is
public API so there is no LocationUnbundled.)

Add an initialization timeout to LocationTimeZoneProviderRequest so that
providers can make intelligent choices about (for example) how long to
spend waiting for geolocation to happen passively.

Test: atest services/tests/servicestests/src/com/android/internal/location/timezone/
Test: atest services/tests/servicestests/src/com/android/server/location/timezone/
Bug: 152744911
Change-Id: Id3e9e6916e8c3a132d8fc892338578ab9d2ff574