Optionally provide EXT_meshopt_compression

[wrangelvid]

For consistency sake, all valid gltf files were converted with gltfpack using the options:
gltfpack -i PATH -o PATH -tr -noq -cf -kn -km -ke

Note that the following files were not valid gltfs:
geometry/render_gltf_client/test/test_color_scene.gltf
geometry/render_gltf_client/test/test_depth_scene.gltf
geometry/render_gltf_client/test/test_label_scene.gltf

This is intended to land after:
meshcat-dev/meshcat#190

Let's see if CI will hate me.

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This change is 

[jwnimmer-tri]

I would say, as we did with #20935, for meshes inside of Drake itself (as opposed to drake_models) we should take a light hand with conversion. Most models in drake should remain simple -- no basisu, no meshopt. It's more important that they be easy to modify for developers, than they be performant for users. Models in this repo are mostly for test cases, not for users or demos. We also need to be sure that some tests have neither compression option in use, so that we know (prove) users' vanilla files will remain working.

I think we just need three changes:

(1) Along the lines of #21090, we should have 1 test file for render engines. Adding a copy of the "fully textured pyramid" for that purpose is probably the right idea, so that all of the "gltf option variant" flavors are in one place.

(2) Along the lines of #21249, changing the scene_graph example sun.gltf to use meshopt compression serves as a nice demo.

(3) Along the lines of #21313, we should have a meshcat_manual_test show an asset (possibly from drake_models) that uses the new feature in a way that eyeball inspection would notice if the feature got broken. Possibly the existing mustard bottle is good enough (assuming it gets changed in drake_models to use the new compression).

Also note that, as with #21193, we will need to update Drake's documentation to explain the newly-available file format.

[wrangelvid]

You are right, I jumped the gun on the converter too soon.
Thank you for the references! Let me convert this PR back to draft, and take some time to bring in the changes more carefully.

Reviewable status: needs platform reviewer assigned, needs at least two assigned reviewers, missing label for release notes (waiting on @wrangelvid)

[jwnimmer-tri]

(It's also OK to close this PR, and re-open once you have a new one ready.)