BGR(A) image format support

[Wumpf]

What

• Fixes Support images in BGR and BGRA #2340

Adds a checklist item that goes through all the different format to make sure they run properly - this looks a bit overzealous, but in fact we are using the fact that wgpu has special support for 8bit bgr images in order to support them on meshes (this detail is tbf untested as of now!), so going through our formats in a test has quite some merit.
(aaalso I think it's the only place where we actually check now that all datatypes still work fine 😳 )

("ethnically sourced lena picture", courtesy of Morten Rieger, https://mortenhannemose.github.io/lena/)

Speaking of meshes: the mesh texture support story is now spelled out better, showing warnings and ignoring textures if they're in an unsupported format.

Checklist

• I have read and agree to Contributor Guide and the Code of Conduct
• I've included a screenshot or gif (if applicable)
• I have tested the web demo (if applicable):
  • Using examples from latest main build: rerun.io/viewer
  • Using full set of examples from nightly build: rerun.io/viewer
• The PR title and labels are set such as to maximize their usefulness for the next release's CHANGELOG
• If applicable, add a new check to the release checklist!
• If have noted any breaking changes to the log API in CHANGELOG.md and the migration guide

• PR Build Summary
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[github-actions]

Deployed docs

Commit	Link
254638f	https://landing-hyhgk0r4g-rerun.vercel.app/docs

[emilk]

⭐

[emilk]

Is using the Bgra8Unorm texture even a good idea, or is it just adding complexity?

[Wumpf]

from the pov of the all knowing rectangle shader it's just extra complexity, so I should add a comment for the rationale of doing this anyways!

The reason is that this allow us to use BGR(A) on meshes and other occasions where we today don't have fancy decoding etc..
This is very very subtly hinted at by the behavior of required_shader_decode which the mesh visualizer uses to determine if it should warn the user that it can't consume a given image.
(in the glorious 🌈 future 🌈 re_renderer will have an internal conversion pipeline that will allow us to do texture conversions separately and gpu accelerated on the fly for all types. But we live in the now and gotta squeeze out the 80% with what we have 😄)

[Wumpf]

for the code, cleaned up and more formalized :)

            // Make use of wgpu's BGR(A)8 formats.
            //
            // From the pov of our on-the-fly decoding textured rect shader this is just a strange special case
            // given that it already has to deal with other BGR(A) formats.
            //
            // However, we have other places where we don't have the luxury of having a shader that can do the decoding for us.
            // In those cases we'd like to support as many formats as possible without decoding.
            //
            // (in some hopefully not too far future, re_renderer will have an internal conversion pipeline
            // that injects on-the-fly texture conversion from source formats before the consumer of a given texture is run
            // and caches the result alongside with the source data)
            //
            // See also [`required_shader_decode`] which lists this case as a format that does not need to be decoded.