Handle light status bar for split-screen

In split-screen the light status bar flag for one side of the
status bar can be different from the other side.
SYSTEM_UI_FLAG_LIGHT_STATUS_BAR is now reported for both
the fullscreen stack and docked stack, but not anymore in the
"default" SysUI visibility field when reporting a visibility
change to SystemUI. The change also reports the docked stack
and the fullscreen stack bounds, so SystemUI can guard tinting
the icons on whether the icon is one of the areas.

When calculating the light status bar flag in PWM, we keep track
of the top fullscreen opaque window state for the docked and
fullscreen stack separately.

Bug: 24365214
Change-Id: Id2240a86d75bf96e0138ec7652a4793859f56e3c