This reflects QWidget API, and restores some behavior from Qt4.
Some WM can have several state at the same time. On Plasma for example,
when a window is both maximized and minimized, the "maximized" checkbox
is checked from the taskbar entry.
The API of QPlatformWindow was changed to take a QFlag and the platform
plugins were adapted.
- On XCB: Always send the full state to the WM. And read the full state.
- On Windows: The code was originally written with '&' in Qt4, and was changed
to == when porting. Some adaptation had to be made so the states would be
preserved.
- On macOS: Only a single state can be set and is reported back for now,
with the possibly to expand this in the future.
- Other platforms: Just do as before with the effective state.
Task-number: QTBUG-57882
Task-number: QTBUG-52616
Task-number: QTBUG-52555
Change-Id: I7a1f7cac64236bbd4c591f796374315639233dad
Reviewed-by: Gunnar Sletta <gunnar@crimson.no>
Reviewed-by: Robin Burchell <robin.burchell@crimson.no>
a02959bb5b