Consider shell transition to update display mode

This continues the purpose of [1] for shell transition. Because
"isAnimating(TRANSITION | PARENTS)" cannot detect the transition
animation which will run by shell.

Also simplify isObscuringDisplay because the split root task can be
fullscreen, but the window in the child task is not, then the condition
can return earlier.

[1]: I5b3ddbc8278a95b4c5239812b2c4a293775c740a

Fix: 267365057
Test: RefreshRatePolicyTest#testAnimatingAppOverridePreferredModeId
Test: Assume device enables 120Hz, launch an app that requests 60Hz.
      And then swipe-up, the animation should run in 120Hz.
Change-Id: I4baba6441dee0dc26ab35456ab916672d69914d9