Merge GDK macOS branch

There is still plenty to do here, which I will be continuing to do as additional MRs.

Such as:

• Remove quartz backend in favor of macos backend.
• Implement GL context and use CAOpenGLLayer for GL renderer
• Convert gtk/ quartz code to GDK_WINDOWING_MACOS
• control/command and other input translations
• Finish DnD/pasteboard implementation
• Media backend for gstreamer/quicktime
• Hi resolution pixel based scrolling for macos touchpad

But at this point, you can run gtk4-demo, gtk4-widget-factory just fine