Fix issue with letterboxing

- Only consider client state if new API is actually turned on.
- We only sent the state the client was actually controlling.
However, we then later check for visibility for state that may not
even exist. Thus, we keep the state but only update the sources
the client is actually controlling.
- Initialize source with default visibility. This prevents
issues where the source may not exist but we still check it.

This fixes issues where a letterbox was accidentally placed on
screen because WM was thinking client requested fullscreen flag
(hiding the status bar), and other places where we checked
requested visibility.

Also renamed client state to requested state.

Test: Open any app, open IME
Bug: 111084606
Change-Id: Ibead561fc5593d8944400320f5e31dbe262612fe