servo: Merge #16893 - Implement WebGL extensions (from MortimerGoro:webgl_extensions); r=emilio

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This PR provides the base for implementing WebGL extensions. It comes with the following ones already implemented and passing all related WebGL conformance tests:

- OES_texture_float
- OES_texture_float_linear
- OES_texture_half_float
- OES_texture_half_float_linear
- OES_vertex_array_object

I'll submit other extensions like compressed textures in a separate PR to ease the review process. I included the 5 extensions in this PR because it's easier to show/review how the WebGL extension base works.

To pass all OES_texture_float_xxx tests I had to add some missing format conversions in WebGLRenderingContext.rs

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- [x] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).

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Source-Repo: https://github.com/servo/servo
Source-Revision: b0976566fb9c79f7dc67b2ac808eb50ef4ad653f

servo/python/tidy/servo_tidy/tidy.py

@@ -58,6 +58,7 @@ FILE_PATTERNS_TO_IGNORE = ["*.#*", "*.pyc", "fake-ld.sh"]
 SPEC_BASE_PATH = "components/script/dom/"
 
 WEBIDL_STANDARDS = [
+    "//www.khronos.org/registry/webgl/extensions",
     "//www.khronos.org/registry/webgl/specs",
     "//developer.mozilla.org/en-US/docs/Web/API",
     "//dev.w3.org/2006/webapi",