Use WindowState for InsetsSourceProvider

This is essentially a revert of [1], modifying InsetsSourceProvider
to use WindowState instead of WindowContainer, as the latter option
is no longer used and required.

  [1]: I8a8385b6688504457a8597afd53ae00a65d4dc42

Flag: EXEMPT cleanup
Bug: 281029564
Bug: 199449177
Test: atest InsetsSourceProviderTest
  ImeInsetsSourceProviderTest
  InsetsStateControllerTest
  WindowTokenTests
Change-Id: I168d55f41d8be2c0b6d38d631f379c2859b8e2c3