Introduce ContentCaptureService metric batching.

This change adds batching of metrics inside ContentCaptureService. Metrics will only be flushed when over a threshold, which will decrease the number of binder calls to the service implementation.

Exact metrics flushing timing:

1) Any Appeared/Disappeared/TextChanged events count over the threshold (if any new content capture events)
2) Session paused (e.g. FG Activity changes)
3) Session finished (e.g. Activity destoryed)
4) Service disconnected (e.g. AiAi crashed, which should be a super rare case)

Bug: 433614684
Flag: android.view.contentcapture.flags.reduce_binder_transaction_enabled
Test: atest android.view.contentcapture.LoginTest
Test: manually tested via Android Data Hub
Change-Id: If7262ede6300031429468b1612c3f3a1082e8361

Change-Id: If7262ede6300031429468b1612c3f3a1082e8361