Introduce TextClassifierEventTronLogger

1. SelectionEvent will be still logged via SelectionSessionLogger
   to make sure we don't break existing logs.

2. New features including language detection and conversation actions
   are logged via TextClassifierEventTronLogger.

3. Added TYPE_ACTIONS_GENERATED to log when actions are generated.
   This is used to calcuate the recall, i.e. among all the requests,
   how many of them TextClassifier returns something.

Test: atest TextClassifierEventTronLoggerTest
Test: Turn on the DEBUG flag and observe the logging.

BUG: 120803809
BUG: 120828422

Change-Id: I33f2ce58885d90bc35316f54abcd42b137b42a13