Use GPU based transfer to do chroma conversions of native decoder output

[Wumpf]

What

• Important chunk of Native AV1 decoding via rav1d/dav1d #7605
• Related to Unify GPU texture conversion (with focus on chroma downsampled formats) #7608
  • todo: create a new ticket for bgr shenanigans and close this one

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Fixes performance issues with our previous inefficient cpu based chroma conversion:

... and fixes color space issues:

Top left: now
Top right: before
Bottom: VLC

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There was an oversight in the conversion pipeline that if fixed now: It only allowed for creating new textures.
Now it can also update existing textures! This means that it takes a target texture from the outside. Naturally, there's some constraints on what the target texture looks like and as a consequence I added some validation for that. Could be more, but I think this is solid enough for our purposes :)

Checklist

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[emilk]

Awesome-sauce!

[emilk]

nice