Let fake control target override visibility received by other windows

Previously, the fake control target could only override the insets
visibility in its own client. But since it was the real target
overriding the real visibility affect all other windows before the
transient control target becomes the real target, it should keep
overriding the visibility when it becomes the fake control target.
Otherwise, that may cause the layout change, and the screen may look
flicker.

Fix: 281740543
Test: atest InsetsPolicyTest
Test: Show Gboard in landscape fullscreen mode on an immersive app,
      press the voice input button, see if the IME layout is changed by
      status bar.
Change-Id: I0bc0c470d0572cd9115ea09c4402580e98db6182