Fix quickswitch flickers/ignored swipes

- Don't set current page to running task when applying load plan,
  if we are already settling on a new task to launch.
- When starting a new task, finish to the running app if that's
  the task being started (should not happen with above change)
- When disabling free scroll mode, don't snap to a page if we're
  already on it. This was setting mNextPage so the first check
  was falsing.

Bug: 142068081
Change-Id: I5b392d9726a81c51718d2f94eee6cd4f78b61f69
Merged-In: I5b392d9726a81c51718d2f94eee6cd4f78b61f69
(cherry picked from commit af33f2c9)
(cherry picked from commit 4d86c804)