Report instant event from CUJ UI thread once started

This will allow to accurately determine which UI thread a CUJ is associated to, and deprecate hardcoded lists.

See aosp/3191152 for metric changes.

Bug: 337803466
Test: Recorded perfetto trace and used with aosp/3187162
Flag: None - logging
Change-Id: Ia771c5f5b246037edfc91d7dae75e82a4ac330cb