Relocate the getInsetsForWindow logic inside WindowState.

- This is done so that the WindowState owns the high level insets logic.
- Will help to implement getInsetsState() in other containers once the
  insets are moved to WindowContainer as part of the hierarchical insets
  effort.

Fix: 207693667
Bug: 199449177
Test: atest WindowStateTests
Test: atest InsetsStateControllerTest
Test: atest DisplayPolicyLayouttyTests
Change-Id: Idb646f6f3730d6d88091ea82b3e80c4701bb477d