Introduce and update interfaces for return animations and takeovers.

WindowAnimationState will be used to transfer the state of a task's
window from Launcher to the Animation lib (through Shell) when a Home
gesture handover happens.

Bug: 323863002
Flag: NA
Test: NA, new methods and interfaces are unused (still builds)
Change-Id: I507246206a86029601c2a4c08f8c7e601b039167