The open source OpenXR runtime

doc: Document !2471

Part-of: <https://gitlab.freedesktop.org/monado/monado/-/merge_requests/2471>

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+1
doc/changes/auxiliary/mr.2471.md
··· 1 + m/relation_history: Introduce an option for "filtered motion vectors" to calculate reasonable motion vectors of noisy input.
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doc/changes/drivers/mr.2471.md
··· 1 + d/hydra: Rewrite to add prediction, relation history, and filtered motion vectors.