Auto merge of #23226 - mmatyas:webgl_compressed_textures, r=jdm

Add initial support for WebGL compressed textures

This patch is an initial implementation of WebGL compressed texture support, it contains

- functions for registering and querying compressed texture extensions
- initial implementation of `CompressedTexImage2D` and `CompressedTexSubImage2D` and their parameter validation
- implementation of S3TC (DXT1, DXT3, DXT5) and ETC1 extensions as examples

What's still missing:

- some of the parameter validation steps are missing
- the pixel comparison tests fail for more complex cases (I'm probably missing something trivial at the GL calls)

Related: #10209 and #20594

cc @jdm @zakorgy

---
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] Related issues: #10209, #20594
- [x] There are tests for these changes

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tests/wpt/webgl/meta/MANIFEST.json

@@ -10888,7 +10888,9 @@
    "conformance/extensions/webgl-compressed-texture-s3tc.html": [
     [
      "conformance/extensions/webgl-compressed-texture-s3tc.html",
-     {}
+     {
+      "timeout": "long"
+     }
     ]
    ],
    "conformance/extensions/webgl-compressed-texture-size-limit.html": [
@@ -27817,7 +27819,7 @@
    "testharness"
   ],
   "conformance/extensions/webgl-compressed-texture-s3tc.html": [
-   "28e3cfc5628760d1ae27166612f17ed46fa12b88",
+   "ea56180224af7537748a649a724563a86c431710",
    "testharness"
   ],
   "conformance/extensions/webgl-compressed-texture-size-limit.html": [