Add tranistion combine trace-events

A common source of transition problems is when
multiple independent actions get combined into a
single transition.

This tries to add some trace events (and logs) around
these situations to help with identifying hotspots and
debugging.

Bug: 325114242
Test: Existing tests, just adding trace.
Flag: EXEMPT adding trace
Change-Id: Ie1180115665a992f22ab273ec1cb4c9d1e68c40b