[HDRP] Fix motion vector computation and compilation issue

[pmavridis]

Purpose of this PR

Fix compilation issue on PS5 (float4x4, float3 multiplication).
Also "Backport" a motion vector computation fix from this PR (#7090)

[github-actions]

Hi! This comment will help you figure out which jobs to run before merging your PR. The suggestions are dynamic based on what files you have changed.
Link to Yamato: https://unity-ci.cds.internal.unity3d.com/project/902/
Search for your PR branch using the search bar at the top, then add the following segment(s) to the end of the URL (you may need multiple tabs depending on how many packages you change)

HDRP
/jobDefinition/.yamato%2Fall-hdrp.yml%23PR_HDRP_trunk
With changes to HDRP packages, you should also run
/jobDefinition/.yamato%2Fall-lightmapping.yml%23PR_Lightmapping_trunk

Depending on the scope of your PR, you may need to run more jobs than what has been suggested. Please speak to your lead or a Graphics SDET (#devs-graphics-automation) if you are unsure.

[github-actions]

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