Compile OpenXR into MacOS build

[BastiaanOlij]

Now that Khronos added OpenXR support on MacOS I've added support for it in Godot even though Apple doesn't do anything with XR on Mac.

As a bonus it nicely solves the issue of the action map editor not being available on Mac. You can developer Quest applications on Mac (and we have various people doing so) but you couldn't configure the action map so that was annoying.

Now obviously with MacOS support for OpenXR there are things in the works. I believe Monado is working on MacOS support which would allow various PCVR headsets to potentially work on Mac, and there are likely other options coming soon.

Bugsquad edit: fixes #79582

[Riteo]

I'm adding support because this nicely solves the issue of the action map editor not being available on Mac.

If I'm understanding correctly this would fix #79582, right?

[BastiaanOlij]

If I'm understanding correctly this would fix #79582, right?

Yup :)

[BastiaanOlij]

I'm putting this up for review because I was just able to verify the OpenXR side of this works (using an OpenXR runtime I can't disclose details off because it may never see the light of day and is unfinished).

[dsnopek]

The code for this looks good to me!

I don't personally have a good way to test it, but for the most common use-case (developing Quest apps from a Mac), basically, if it compiles it works. And I can see it compiling fine in the "macOS / Template" build on CI:

https://github.com/godotengine/godot/actions/runs/5588692055/job/15136001454?pr=79614

🚀 Ship it! 😄

[fire]

Ship it!

I and aaronfranke use macs often and there's a series of differences between platforms.

[YuriSizov]

Thanks!

[BastiaanOlij]

Marked this for cherry picking in 4.1, we're not sure what changed in 4.1 but before the only problem we had was not being able to edit the action map. In the latest 4.1 builds some people have reported issues exporting on Mac due to missing classes that are part of the OpenXR module.

This PR solves that issue on 4.1

[YuriSizov]

Cherry-picked for 4.1.4.