This commit implements WebGL's:
* cullFace
* frontFace
* enable
* disable
* depthMask
* colorMask
* clearDepth
* clearStencil
* depthFunc
* depthRange
* hint
* lineWidth
* pixelStorei
* polygonOffset
* texParameteri
* texParameterf
* texImage2D (partially)
It inlines a lot of OpenGL calls to keep the file
`components/canvas/webgl_paint_task.rs` as small as possible while
keeping readability.
It also improves error detection on previous calls, and sets node damage
on the canvas in the drawing calls.
It adds a `TexImage2D` reftest, even though it's not enabled because:
* WebGL paints the image when it loads (asynchronously), so the reftest doesn't wait for it and it finishes early
* If we change the source for the base64 src of the image it works as expected in non-headless mode, but the test harness locks
To actually make the multiprocess communication work, we'll need to
reroute the task creation to the pipeline or the compositor. But this
works as a first step.
This improves the encapsulation and consistency in our WebGL
implementation.
Also allows to implement new methods such as `getShaderSource()`.
It will also allow us to use `delete()` in the destructors of them (note
that we will want to keep track of them from the context).
