Batching API batch retrieval changes

Allows one last batch of fixes, if available, be retrieved by HIDL
client after stop() is called. Also, if flush() is called, service
end will always report something, empty if no more fixes in the
batch.

Bug: 180602917
Test: atest CtsLocationFineTestCases:android.location.cts.fine.LocationManagerFineTest#testRequestFlush_Gnss
CRs-fixed: 2870223
Change-Id: Ib6e47a601f881b79ae459b163da5bbf04bf24f52
3 files changed