Add APIs to add/remove local InsetsSourceProviders in WindowContainer.

- updateAboveInsetsState() now updates the entire hierarchy everytime
  it is called.
- updateAboveInsetsState() also takes care of passing the local Insets
  Sources to the insets-state of every children in the subtree of the
  WindowContainer for which the API was called.
- addLocalInsetsSourceProvider() adds a new local InsetsSourceProvider
  to the WindowContainer.
- removeLocalInsetsSourceProvider() removes a local InsetsSourceProvider
- Made InsetsSourceProvider abstract and added a
  WindowContainerInsetsSourceProvider to be used instead. Eventually
  all the window specific logic will be moved to WindowContainerInsets-
  -SourceProvider.

Bug: 199449177
Test: atest InsetsStateControllerTest WindowContainerTests WindowManagerServiceTests
Test: atest ActivityRecordTests
Change-Id: I8d93b739df6d5f18a0d2219d9b00d96a2829746c