OpenXR: Register eye gaze even when disabled

[BastiaanOlij]

When we added the option to gate certain extensions, we implemented this such that the extension is not registered at all.
For the eye gaze interaction extension we need to make an exception because this extension also registers meta data for our action map. If it doesn't do this our action map UI will fail when interactions have been added to the action map, but the action map UI is unable to make sense of this.
Instead the extension simply remains disabled.

Fixes #86358

[dsnopek]

The code looks good to me, and it fixes the issue in my testing!

From one of your earlier comments:

There is also a question whether it makes sense to add the eye gaze interaction to the default action map. I think we should remove that bit.

This PR doesn't do that. Should we add that here?

What's here already is great, so I don't think that should necessarily hold it back - we could certainly do that in a follow-up PR as well.

[BastiaanOlij]

@dsnopek for now I decided to keep it in the action map. The problem with removing it is that when someone enabled eye gaze interaction, it won't immediately work. While part of me in answer to that says RTFM, seeing it is now properly filtered out it doesn't do much harm.

[akien-mga]

Thanks!

[dsnopek]

@BastiaanOlij Ok, sounds good!