Restore content surface to transition root when animation finishes

In case the finish transaction won't apply immediately if there are
subsequent transitions to run, e.g. DefaultMixedHandler. Otherwise
before the finish transaction applies, the screen may be black
because the parent of content surface is removed.

The transition surface hierarchy when performing rotation animation
with visible wallpaper (back effect only creates for the case):
 Transition root
  > Back effect (background color for windowing layer)
   > Windowing layer (the content, i.e. mSurfaceControl)

Bug: 411163941
Flag: EXEMPT  bugfix
Test: While holding device in landscape, enter split screen
      from portrait home. There won't flash a black screen.

Change-Id: I93f95ac05e2233e4492f0461cdfff7f84b94bde8
Signed-off-by: buwenjing <buwenjing@xiaomi.com>