[ShellTransition]: add WMS#setRecentsAppBehindSystemBars for recents

For legacy recents animation, launcher side use
RecentsAnimationController#setAnimationTargetsBehindSystemBars to
callback if the animating recents task target is valid to affect
system bar apparence according the gesture threadshold.

if the animating recents task is behind system bar, means the
gesture threshod not yet passed and the task still can affect
system bar apparence, and vice-versa.

with shell-transition, since launcher triggers recents animation
by normal startActivity without initiating RecentsAnimationController
with startRecentsActivity, the launcher will be top-resumed
(but the surface hierarchy the recents task is still be top-most) when
starting gesture on navbar, in this case, launcher can affect the
system appearence even though launcher is behind systembar.

beside, previously we also rely on setAnimationTargetsBehindSystemBars
to hide soft-keyboard in multi-windowing mode when quick-swich tasks,
without this, soft-keyboard will keep visible when swiping up to
recents.

As the result, we needs to backport the most logic of
setAnimationTargetsBehindSystemBars for fixing the above cases,
the only difference is we renaming the method with
setRecentsAppBehindSystemBars(behindSystemBars) to only set recents app
can affect systembar apparence, and placing hide IME/IME icon logic into
handleLegacyRecentsStartBehavior when starting recents animation.

Fix: 215504556
Test: manual as below CUJs with enabling shell-transition:
 CUJ1:
  1) Launching a app with showing IME
  2) Quick-switching to the next task or swiping task to home
  3) Expect no navbar icon flickering

 CUJ2:
  1) With entering split-screen and showing IME on the split task
  2) Swipe up to recents
  3) Expect IME shound be hidden

 CUJ3:
  1) Launching a app
  2) Hammer tapping on the navigation bar
  3) Expect the staus bar icon won't blinking

Change-Id: I552eea738aed5566eb897bb9c68507e83ac43e1d