Fix registerListener and flush bugs.

1) Fix registerListener to return false when called with a Trigger sensor. Correct java documentation.
2) Remove reservedFlags and FlushCompleteListener parameters from the public API.
3) Create SensorEventListener2 which extends SensorEventListener and has the onFlushCompleted callback.
3) Change flush(Sensor) API to flush(SensorEventListener).

Change-Id: I56ce4e0b6e329483e129a14ad7e8a0cd35665ffe
Bug: 10894703