macOS: Disable minimize button for Qt::Dialog windows by default

Regression after 4c78ef80ca, where
we moved the window titlebar button logic from QCocoaWindow's
windowStyleMask function to updateTitleBarButtons.

Fixes: QTBUG-114064
Pick-to: 6.5
Change-Id: Idb0870571e88fa2962af36decd9bc7b53c35664d
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>

src/plugins/platforms/cocoa/qcocoawindow.mm

@@ -553,10 +553,17 @@ void QCocoaWindow::updateTitleBarButtons(Qt::WindowFlags windowFlags)
 
     bool hideButtons = true;
     for (const auto &[button, buttonHint] : buttons) {
+        // Set up Qt defaults based on window type
         bool enabled = true;
+        if (button == NSWindowMiniaturizeButton)
+            enabled = window()->type() != Qt::Dialog;
+
+        // Let users override via CustomizeWindowHint
         if (windowFlags & Qt::CustomizeWindowHint)
             enabled = windowFlags & buttonHint;
 
+        // Then do some final sanitizations
+
         if (button == NSWindowZoomButton && isFixedSize())
             enabled = false;