Auto merge of #25025 - Manishearth:originOffset, r=jdm
Auto merge of #25025 - Manishearth:originOffset, r=jdm

Origin offset fixes

https://github.com/immersive-web/webxr/issues/567 was closed out. We were computing offset spaces of already-offset spaces incorrectly, but otherwise our math is correct. I improved our comments around this with more math, so I never have to do this math again.

Chrome's math isn't, which is why we fail some tests around this: https://bugs.chromium.org/p/chromium/issues/detail?id=1030049 . I'm planning to wait for them to fix and upstream the tests, I've already verified that we pass the corrected test.

r? @jdm

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