Reduce operations before dispatching transition ready

This avoids the latency by logging for TransitionTracer before
notifying shell that the transition is ready.

Also use calculated info for tracer to avoid overhead such as
getChangeFlags may need to traverse the window hierarchy again.

Bug: 275508603
Test: Check trace that the start of Transition's "playing"
      can appear earlier in "onTransactionReady".
Change-Id: I2c21d3e4f8bfe18e43c14f84428d13a6758c7b8d