Add ShowDirectoriesFirst platform theme hint

This allows Qt Quick Dialogs to accurately check how it should show
files and directories.

Change-Id: I0f5102553ff9a0484b3714ba176f7e5e668fd05c
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

src/gui/kernel/qplatformtheme.cpp

@@ -167,6 +167,10 @@ QT_BEGIN_NAMESPACE
                         as basis for the resize.
                         This enum value has been added in Qt 6.2.
 
+    \value ShowDirectoriesFirst (bool) Whether directories should be shown
+           first (before files) in file dialogs.
+           This enum value was added in Qt 6.2.
+
     \sa themeHint(), QStyle::pixelMetric()
 */
 
@@ -574,6 +578,8 @@ QVariant QPlatformTheme::defaultThemeHint(ThemeHint hint)
         return QVariant(10);
     case InteractiveResizeAcrossScreens:
         return true;
+    case ShowDirectoriesFirst:
+        return true;
     }
     return QVariant();
 }

src/gui/kernel/qplatformtheme.h

@@ -119,6 +119,7 @@ public:
         IconFallbackSearchPaths,
         MouseQuickSelectionThreshold,
         InteractiveResizeAcrossScreens,
+        ShowDirectoriesFirst,
     };
 
     enum DialogType {

src/plugins/platforms/cocoa/qcocoatheme.mm

@@ -527,6 +527,8 @@ QVariant QCocoaTheme::themeHint(ThemeHint hint) const
         return QVariant(bool([[NSApplication sharedApplication] presentationOptions] & NSApplicationPresentationFullScreen));
     case QPlatformTheme::InteractiveResizeAcrossScreens:
         return !NSScreen.screensHaveSeparateSpaces;
+    case QPlatformTheme::ShowDirectoriesFirst:
+        return false;
     default:
         break;
     }