Implement WEBGL_debug_shaders

[MrX1980]

Mozilla has implemented WEBGL_debug_shaders on 2014-02-13
https://bugzilla.mozilla.org/show_bug.cgi?id=968374

[emackey]

We list this, in the list of extensions at the bottom. Is anything more needed here?

[pjcozzi]

See https://www.khronos.org/registry/webgl/extensions/WEBGL_debug_shaders/

We could, for example, have a text box where the user copies and pastes a vertex and fragment shader and then we display the HLSL (assuming ANGLE). I think this is outside the scope of WebGL Report so I am OK closing this. It could be a cool separate tool though, but for our work in Cesium, I would want support for this directly in the engine.