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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components/script/dom/webidls/WEBGLCompressedTextureETC1.webidl

@@ -0,0 +1,13 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+/*
+ * WebGL IDL definitions from the Khronos specification:
+ * https://www.khronos.org/registry/webgl/extensions/WEBGL_compressed_texture_etc1/
+ */
+
+[NoInterfaceObject]
+interface WEBGLCompressedTextureETC1 {
+    /* Compressed Texture Format */
+    const GLenum COMPRESSED_RGB_ETC1_WEBGL = 0x8D64;
+}; // interface WEBGLCompressedTextureETC1

components/script/dom/webidls/WEBGLCompressedTextureS3TC.webidl

@@ -0,0 +1,16 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+/*
+ * WebGL IDL definitions from the Khronos specification:
+ * https://www.khronos.org/registry/webgl/extensions/WEBGL_compressed_texture_s3tc/
+ */
+
+[NoInterfaceObject]
+interface WEBGLCompressedTextureS3TC {
+    /* Compressed Texture Formats */
+    const GLenum COMPRESSED_RGB_S3TC_DXT1_EXT  = 0x83F0;
+    const GLenum COMPRESSED_RGBA_S3TC_DXT1_EXT = 0x83F1;
+    const GLenum COMPRESSED_RGBA_S3TC_DXT3_EXT = 0x83F2;
+    const GLenum COMPRESSED_RGBA_S3TC_DXT5_EXT = 0x83F3;
+}; // interface WEBGLCompressedTextureS3TC