The window stack will now upkeep three groups of windows, always
on bottom (1), regular (2), always on top (3). Windows belonging to
(3) will always appear on top of (2) and (1), and windows from (2) will
always appear on top of (1).
The first window created in the application gets the (1) status, which
is in line with the root window mechanism used before.
Activation has now been decoupled from the top position on the window
stack as a window in (1) or (2) may be active, in spite of the top
window belonging to a higher group.
Fixes: QTBUG-110098
Change-Id: I51f4d2d47163fab26ce5ef28f7a4f23a522c7f91
Reviewed-by: Lorn Potter <lorn.potter@gmail.com>
a596ea0fe2