Centering freeform window after transition

Currently, when we drag a fullscreen window from the top to transition
it into a freeform window, the freeform bounds are set based on where we
release the window. This change animates it to the center instead.

Bug: 266973706
Test: Manual Testing
Change-Id: I1877ccbecbae51926e7dee413557417c5f5b5b5e