[DRAFT] Record XrSim tests for the composition layer and passthrough sample projects

[dsnopek]

Now that we have tests via the Meta XR Simulator, this PR is adding tests for the two sample projects that are currently in the repo.

Some notes:

• Cylinder composition layers don't work quite right in the simulator - it's like the faces are wound in reverse, such that it gets back face culled when looking in the correct direction (but the layer is visible when looking in the opposite direction)
• Only basic passthrough is supported by the simulator - geometry passthrough and all the styles don't work
• I had to downgrade to v64 of the simulator because passthrough wasn't working
• Since we have to update the simulator version in the CI manually, we'll be able to update the VRS files if/when the above bugs are fixed (and the current VRS files can help us notice when those bugs are fixed, since the tests will fail)

This is a draft since I don't think the CI is going to work on the first try because I reorganized some things. :-) Once it's working, I'll take it out of draft. (Also, I'm temporarily basing this on PR https://github.com/GodotVR/godot_openxr_vendors/pull/149 to make iteration faster.)

[dsnopek]

Question: Should we use Git LFS for the *.vrs files?

They don't get that big, but if you make one that takes more than ~2 screenshots, they can get big-ish. The one for the passthrough sample on this PR is 57mb (I think I took 5 screenshots?). If we make a couple of revisions to that, it'll start to add up in the overall repo size when doing a full clone. The other *.vrs files are smaller: 5.9mb and 16mb (I only took 1 or 2 screenshots)

I'm personally leaning towards using Git LFS, but since we aren't using it at all in this repo yet, I wanted to run it by other folks first!

/cc @m4gr3d @devloglogan @BastiaanOlij

[devloglogan]

Seeing that any .vrs files we add potentially need to be updated if the related sample/feature is changed, and that "more than ~2 screenshots" feels like an extremely low bar to hit for having a large file, I'd agree that git LFS seems like the right choice.