Add macOS & Wayland events for trackpad zoom and rotate gestures

[pfgithub]

Implements #90 for macOS with two new events: TrackpadZoom and TrackpadRotate. These events can also be implemented for Windows and Linux X11/Wayland, but I do not have a way to test those platforms. Zoom will need to make sure to use a similar scale on all platforms and rotate should use degrees.

• Change log entry in README.md, listing all new symbols
• News page entry, briefly describing the feature
• Guide documentation, with minimal examples, in the relevant guide
• Reference documentation, with all applicable tags
• Cross-references and mentions in appropriate places
• Credits entries for all authors of the feature
• If it adds a new callback, support for it must be added to tests/event.c.

[cblc]

Please, merge this 🙏 🙏 🙏 I really want Magic Trackpad gestures in my apps...

[pfgithub]

I added wayland support, but I'm not really sure where to call _glfwAddPointerGesturesListeners from. The current place works it seems. Also, this needs a rebase to be mergable.