Auto merge of #16893 - MortimerGoro:webgl_extensions, r=emilio

Implement WebGL extensions

<!-- Please describe your changes on the following line: -->

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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- [x] There are tests for these changes OR
- [ ] These changes do not require tests because _____

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Cargo.lock

@@ -1116,6 +1116,11 @@ dependencies = [
  "libc 0.2.22 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "half"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "harfbuzz-sys"
 version = "0.1.7"
@@ -2323,6 +2328,8 @@ dependencies = [
  "euclid 0.11.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "fnv 1.0.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "gfx_traits 0.0.1",
+ "gleam 0.4.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "half 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "heapsize 0.3.9 (registry+https://github.com/rust-lang/crates.io-index)",
  "heapsize_derive 0.1.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "html5ever 0.16.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -3511,6 +3518,7 @@ dependencies = [
 "checksum gleam 0.4.5 (registry+https://github.com/rust-lang/crates.io-index)" = "a86944a6a4d7f54507f8ee930192d971f18a7b1da526ff529b7a0d4043935380"
 "checksum glob 0.2.11 (registry+https://github.com/rust-lang/crates.io-index)" = "8be18de09a56b60ed0edf84bc9df007e30040691af7acd1c41874faac5895bfb"
 "checksum glx 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)" = "b280007fa9c7442cfd1e0b1addb8d1a59240267110e8705f8f7e2c7bfb7e2f72"
+"checksum half 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)" = "63d68db75012a85555434ee079e7e6337931f87a087ab2988becbadf64673a7f"
 "checksum harfbuzz-sys 0.1.7 (registry+https://github.com/rust-lang/crates.io-index)" = "6b76113246f5c089dcf272cf89c3f61168a4d77b50ec5b2c1fab8c628c9ea762"
 "checksum heapsize 0.3.9 (registry+https://github.com/rust-lang/crates.io-index)" = "556cd479866cf85c3f671209c85e8a6990211c916d1002c2fcb2e9b7cf60bc36"
 "checksum heapsize_derive 0.1.4 (registry+https://github.com/rust-lang/crates.io-index)" = "46f96d52fb1564059fc97b85ef6165728cc30198ab60073bf114c66c4c89bb5d"