Update glTF 2.0 demo for 'KHR_texture_basisu'

[donmccurdy]

The glTF WebGL demo currently has an old reference to "a hypothetical GOOGLE_texture_basis extension", written prior to the availability of the official KHR_texture_basisu extension for glTF. This PR updates the demo, model, and documentation to use the official workflow.

I converted the existing .basis image by:

1. basisu image.basis
2. Manually replace the .basis reference with .png reference in .gltf file
3. Compress with gltf-transform etc1s input.gltf output.gltf

I've also removed broken links to demos – if there's a GitHub pages demo published somewhere we could link to that instead?

[richgel999]

Hmm - appveyor failed. Looks like we're seeing a failure on the formatting rules for this PR - any ideas?

*** The following differences were found between the code and the formatting rules:
diff --git a/webgl/gltf/assets/AgiHqSmall.gltf b/webgl/gltf/assets/AgiHqSmall.gltf
index 5bf4f8c..a2ffa38 100755
--- a/webgl/gltf/assets/AgiHqSmall.gltf
+++ b/webgl/gltf/assets/AgiHqSmall.gltf
@@ -198,4 +198,4 @@
"extensionsRequired": [
"KHR_texture_basisu"
]
-}
\ No newline at end of file
+}
*** Aborting, please fix your commit(s) with 'git commit --amend' or 'git rebase -i '

[donmccurdy]

Fixed — I added the missing newline at the end of the file.