Use task position for transition in freeform mode

In freeform mode, the stack bounds equal to display size. To animate
at correct place in this case, it should use the position of task.

Bug: 117596112
Test: atest AppWindowTokenTests#testTransitionAnimationPositionAndBounds
Change-Id: Ib7820196a87e155c6fca040c4e5288dd0a74c763
2 files changed