Not clear if sRGB rendering supported to framebuffer objects in WebGL 2

The only documentation for `framebufferTexture2D` is in the WebGL 1.0 spec. which points to the OpenGL ES 2.0 spec. which supports only four color-renderable formats not including SRGB8. The WebGL 2.0 spec does not indicate any differences from 1.0 that I could spot w.r.t either `framebufferTexture2D` or framebuffer completeness. Therefore it is unclear if the much larger set of color-renderable texture formats required by OpenGL ES 3.0 is supported in WebGL 2.0.

Start by comparing the WebGL 1.0 and WebGL 2.0 specifications around framebufferTexture2D, framebuffer completeness, and color-renderable formats. Check the OpenGL ES 2.0 and 3.0 references cited in the issue; done means the WebGL 2.0 specification clearly states whether SRGB8 and the expanded formats are supported.

Written by the indexing model from the issue text.