QCocoaWindow::windowStyleMask: make popups non-resizable

Otherwise, context menu can be resized.

Pick-to: 6.4 6.2
Task-number: QTBUG-106925
Change-Id: I409d0113fd92ca89b14f068c391dd9c0ddb79ce7
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

src/plugins/platforms/cocoa/qcocoawindow.mm

@@ -526,9 +526,11 @@ NSUInteger QCocoaWindow::windowStyleMask(Qt::WindowFlags flags)
     // working (for example minimizing frameless windows, or resizing
     // windows that don't have zoom or fullscreen titlebar buttons).
     styleMask |= NSWindowStyleMaskClosable
-               | NSWindowStyleMaskResizable
                | NSWindowStyleMaskMiniaturizable;
 
+    if (type != Qt::Popup) // We only care about popups exactly.
+        styleMask |= NSWindowStyleMaskResizable;
+
     if (type == Qt::Tool)
         styleMask |= NSWindowStyleMaskUtilityWindow;