Refactor BubblesTransitionObserver#onTransitionReady.

Moved loop-invariant checks out of the main loop in `onTransitionReady`.
Conditions related to the overall bubble state are now evaluated once
upfront, allowing for an early return if no further processing is
needed.

Additionally, values constant across loop iterations, such as the
expanded bubble's task ID and the bubble view's display ID, are now
pre-computed. This avoids redundant calculations and improves
performance and readability.

BUG: 387193964
Test: atest WMShellUnitTests:BubblesTransitionObserverTest
Flag: EXEMPT refactor
Change-Id: Ib13534ec28b9b2a5bde19a7cfbda75ced48b0f6a