End the attaching animation early when we settle on the end target

The attaching animation can take longer than the transition to recents
when you let go, and the ADJACENT_PAGE_OFFSET calculation is different
when there's a running task vs not. So after the transition to recents
ended, the calculation of the still playing attaching animation would
change, causing the jump you see in the bug. Now we make sure to end
the attaching animation if it's still running when we settle on an
end target to avoid this issue.

Fixes: 168563692
Change-Id: I3f37aecf9c93f2ec63dbdce561e7f5ba11be89cc
Merged-In: I3f37aecf9c93f2ec63dbdce561e7f5ba11be89cc
(cherry picked from commit 1cc12ebc)
(cherry picked from commit fd54a8e8)