OpenXR add core support for Khronos loader

[BastiaanOlij]

This PR adds support for the Khronos OpenXR loader to the core of Godot.

This means that as long as the headset supports it, and you don't use any vendor features or have features locked behind vendor specific manifest entries, Godot can export to a headset without needing the vendor plugin.

All you need to do is enabled Use Gradle Build:

And set the XR Mode to OpenXR:

And your game can be successfully exported to AOSP devices.

Tested on:

• Quest 3
• Pico 4 Ultra

Contributed by Khronos Group through the Godot Integration Project

[BastiaanOlij]

cc @dsnopek @m4gr3d

[BastiaanOlij]

I'm taking this out of draft as it is working. This should not be merged until after we've updated the OpenXR version in the thirdparty folder to atleast 1.1.46

Opinion among the XR team is to also hold off merging until Godot 4.5 has been released as accompanying changes on the vendor plugin side will require some guidance.

[BastiaanOlij]

Rebased so it should now automatically pick up the OpenXR loader for 1.1.47 :)

[BastiaanOlij]

Just discussed with @m4gr3d , need to rebase this and we're planning on removing the custom loader option as there currently is no scenario where we need this.

[BastiaanOlij]

This has now been rebased and I've removed the custom option. PR still works as expected.

Also as expected, with the current vendor plugin installed gradlew complains that we're including the loader twice. While we plan to remove the loader code from the vendor plugin, we want to be backwards compatible so we're looking into manifest changes that tell gradlew to ignore the loader from the vendor plugin.

Once that is resolved this can be merged.