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

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).

<!-- Either: -->
- [x] There are tests for these changes OR
- [ ] These changes do not require tests because _____

<!-- Also, please make sure that "Allow edits from maintainers" checkbox is checked, so that we can help you if you get stuck somewhere along the way.-->

<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/16893)
<!-- Reviewable:end -->

1 files changed, 2 insertions, 0 deletions

diff --git a/components/script/dom/mod.rs b/components/script/dom/mod.rs
index 62bffbdcbcd..bb5f5bf1a71 100644
--- a/components/script/dom/mod.rs
+++ b/components/script/dom/mod.rs
@@ -451,6 +451,8 @@ pub mod vrfieldofview;
 pub mod vrframedata;
 pub mod vrpose;
 pub mod vrstageparameters;
+pub mod webgl_extensions;
+pub use self::webgl_extensions::ext::*;
 pub mod webgl_validations;
 pub mod webglactiveinfo;
 pub mod webglbuffer;