This includes:
1. Provide NetworkStatsRecorder#importCollectionLocked to
allow caller to write a NetworkStatsCollection object to
a standalone file.
2. Do not clear the collection in NetworkStatsRecorder#
CombiningRewriter, this is safe since pending set will
still be cleared during forcePersistLocked.
3. Implement the migration process, including recovery and
safety measures.
Test: NetworkStatsServiceTest NetworkStatsCollectionTest
Test: manual test with
adb shell device_config put tethering \
netstats_store_files_in_apexdata true
adb shell device_config put tethering \
netstats_import_legacy_target_attempts 1
Bug: 230289468
Change-Id: Ic2002cbfd5a6b3c2226fa8dab22481f8ce656574
Merged-In: Ic2002cbfd5a6b3c2226fa8dab22481f8ce656574
(pure cherry-picked from ag/18367994)
a388d4bf06