WebGL linear backbuffer and wide gamut output

Currently, all output of WebGL rendering is either treated as if it's in sRGB or in the display's color space (depending on browser and OS). That is, no conversion is done between fragment shader output and the values sent to the screen.

For linear rendering pipelines - in which rendering is done in linear space - it would be beneficial for engines/applications to be able to output their rendering results from the fragment shader in linear space, and have this remapped this into the display's color space. Currently, the application must do its own conversion from linear space to sRGB. (Plus this doesn't allow applications to take advantage of wide-gamut displays.)

For Canvas, a color space proposal exists here:
https://github.com/WICG/canvas-color-space/blob/master/CanvasColorSpaceProposal.md
I expect that color space support will be added to WebGL canvases in a very similar way.

Start by reading the linked WICG CanvasColorSpaceProposal.md to understand the proposed color-space model and how it may apply to WebGL canvases. The issue is complete when WebGL has a reviewed approach for linear backbuffers and wide-gamut display output, with the required specification and implementation scope established.

Written by the indexing model from the issue text.