New metrics fields for selection logs

Changes that affect logging:
- Switched to new category/actions/fields that are used exclusively by
  selection logging.
- Action types are now logged in the tron type (the information that was
  previously in the field could be derived from other fields).
- Entity types are now logged in the tron sub type.
- Delta time from previous event is now zero for first event (was time
  since epoch).
- The smart select model version is now written for all events after
  smart select has run. (i.e. better support for analysis based on
  terminal events alone)
- Restoring the logging removed in ag/2901629.

Internal only changes:
- Made debug statement conditional on DEBUG_LOG_ENABLED.
- Reduced logging tag length to fit into 23char limit.

Bug: 64914512
Test: Manually tested that logs are correct. Will follow up with automated tests.
Merged-In: If12daa2f206fb42be53587decbe2c4abfd689f41
Change-Id: Iec0f6cf1f9f2efdc8518133cf8551cd96b095ad8