Fix #290946 - Change macOS window title bar color for Dark theme

Previously, when you selected MuseScore's Dark theme,
the title bars of the windows on macOS stayed light.
Now, they will also change, along with the MuseScore theme.

mscore/macos/cocoabridge.h

@@ -27,6 +27,7 @@ class CocoaBridge
    public:
       static void setAllowsAutomaticWindowTabbing(bool flag);
       static bool isSystemDarkTheme();
+      static void setWindowAppearanceIsDark(bool flag);
 };
 
 #endif

mscore/macos/cocoabridge.mm

@@ -31,3 +31,9 @@
     NSString *osxMode = [[NSUserDefaults standardUserDefaults] stringForKey:@"AppleInterfaceStyle"];
     return ([osxMode isEqualToString:@"Dark"]);
 }
+
+void  CocoaBridge::setWindowAppearanceIsDark(bool flag)
+{
+    if (@available(macOS 10.14, *))
+        [NSApp setAppearance:[NSAppearance appearanceNamed:flag ? NSAppearanceNameDarkAqua : NSAppearanceNameAqua]];
+}

mscore/musescore.cpp

@@ -7421,6 +7421,11 @@ void MuseScore::updateUiStyleAndTheme()
       {
       // set UI Theme
       QApplication::setStyle(QStyleFactory::create("Fusion"));
+
+#ifdef Q_OS_MAC
+      // On Mac, update the color of the window title bars
+      CocoaBridge::setWindowAppearanceIsDark(preferences.isThemeDark());
+#endif
 
 #if defined(WIN_PORTABLE)
       QString wd = QDir::cleanPath(QString("%1/../../../Data/%2").arg(QCoreApplication::applicationDirPath()).arg(QCoreApplication::applicationName()));