Auto merge of #24473 - mmatyas:webgl_fns_buffer, r=jdm

Implement the basic WebGL2 buffer data operations

Adds support for the WebGL2 calls `bufferData`, `bufferSubData`, `copyBufferSubData` and `getBufferSubData`.

Reference: https://www.khronos.org/registry/webgl/specs/latest/2.0/#3.7.3

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This patch depends on https://github.com/servo/sparkle/pull/8. Some tests cause a crash for me at the moment, as they depend on other, not yet implemented buffer calls and transform feedback objects.

As for the code, there are a few parts I'm not sure about:

- To get the element byte size of a TypedArray I've wrote a simple `match`, as the relevant field is not published in `rust-mozjs`. Is that okay or there's some other way to get this already?
- The WebGL1 BufferData implementations were copied into the WebGL2 code as a workaround, due to the difference in the available buffer slots (ie. `self.bound_buffer`). An alternative could be is to pass this function and self as parameters to an internal buffer data implementation function, but personally I found that code to be quite ugly.

cc @jdm @zakorgy

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