UI: Don't mark all widgets in main window as native on macOS

This significantly improves undocking behaviour on macOS for most docks.
Previously, undocking would perform an undock rather than undock + drag.
This does not fix the behaviour for browser docks as they are native.

May also improve performance of the main window, regardless of dock state.

See qt/qtbase@3224c6d

UI/obs-app.cpp

@@ -1536,6 +1536,10 @@ bool OBSApp::OBSInit()
 		native->nativeResourceForIntegration("display"));
 #endif
 
+#ifdef __APPLE__
+	setAttribute(Qt::AA_DontCreateNativeWidgetSiblings);
+#endif
+
 	if (!StartupOBS(locale.c_str(), GetProfilerNameStore()))
 		return false;