WindowInsetsAnimationController: Add state callback and getters

Adds more comprehensive callbacks and getters for the WindowInsetsAnimationController,
to make it more straight forward to properly use.

Test: atest InsetsControllerTest PendingInsetsControllerTest
Fixes: 151707442
Change-Id: Ida55f609112396c0f6de4c5c4431e0793c2e315e