Using terminate() kills the whole process instead of just stopping the event loop, so we're back to the 'old' way.
However, if the provided function finishes too early, that can also fail (will call stop() on a not-yet-running NSApp).
Creating a delegate and waiting for the callback makes sure NSApp is running before the actual main() is called.
Also, for whatever reason only tutorials were changed to use terminate(). Now both tutorials and examples are
using identical code.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer-rs/-/merge_requests/1378>
This is required for OpenGL to work nowadays on macOS. Simply running an
CFRunLoop on the main thread is not sufficient.
Thanks to Philippe Normand for testing this on macOS and making sure it
actually compiles and works.
