Quick change to unblock launching freeform from overview

- Finish the recents animation before starting the freeform task
- Remove MultiWindowFactory abstraction now that freeform is the only
  implementation that uses that

Bug: 239429564
Test: Enable freeform in developer options, launch task into freeform
      from overview

Change-Id: I48069aee322f6a275d2cdae5345b196f8d682bac
Signed-off-by: Winson Chung <winsonc@google.com>