macOS: Don't use full screen geometry for popups

The fullscren geometry when an application is in full screen includes
the area above the menu bar. Unfortunately, when clicking on areas of
a Qt popup that overlays the menu bare area we get a callback for
NSMenuDidBeginTrackingNotification, and as a result we close all
popups. As macOS for some reason treats the menu bar area as special
and tracks clicks there even if another window is on top, we should
not put our popups there.

This also matches the geometry of windows shown full screen, which
does not overlap the menu bar area either when using the native APIs
to make a window fullscreen (which we do).

This change does not affect the original issue (QTBUG-39403), as the
QScreen::availableGeometry() nowadays does not exclude the area of
the Dock when in fullscreen mode.

Pick-to: 6.8 6.7 6.5
Task-number: QTBUG-39403
Fixes: QTBUG-123298
Change-Id: I5890d7fc7a9b95a98b8fd2b9ce58ed9789e7f36e
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

src/plugins/platforms/cocoa/qcocoatheme.mm

@@ -453,7 +453,7 @@ QVariant QCocoaTheme::themeHint(ThemeHint hint) const
     case QPlatformTheme::SpellCheckUnderlineStyle:
         return QVariant(int(QTextCharFormat::DotLine));
     case QPlatformTheme::UseFullScreenForPopupMenu:
-        return QVariant(bool([[NSApplication sharedApplication] presentationOptions] & NSApplicationPresentationFullScreen));
+            return false;
     case QPlatformTheme::InteractiveResizeAcrossScreens:
         return !NSScreen.screensHaveSeparateSpaces;
     case QPlatformTheme::ShowDirectoriesFirst: