Auto merge of #25905 - szeged:mmatyas__webgl_fns_read_draw_buffers, r=nox

Add support for WebGL2 read and draw buffer settings

Adds support for the `ReadBuffer` and `DrawBuffers` WebGL2 calls and the related parameter getters.

See:

- https://www.khronos.org/registry/webgl/specs/latest/2.0/#3.7.2
- https://www.khronos.org/registry/webgl/specs/latest/2.0/#3.7.4
- https://www.khronos.org/registry/webgl/specs/latest/2.0/#3.7.11

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This is marked as WIP because with these functions added (but apparently not directly related to them), some tests now run into states that produces crash.

cc @jdm @zakorgy

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- [x] There are tests for these changes

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