Add WebGL extensions

[Elchi3]

#1583 decided to put some WebGL extensions in the main WebGL feature but not all of them. I think no WebGL extension should be with the main WebGL feature. The extensions have very different support, some are meant to be for certain operating systems only (mobile only, for example), some require specific drivers, etc. I think it is best if they stand on their own. I introduced a "webgl-extensions" group to keep them together.

Still to be done are the descriptions, but would be nice to get a 👍 on the approach here before writing all of them.

[Elchi3]

@ddbeck are you okay with the "The EXT_color_buffer_half_float extension to WebGL TODO" structure for the descriptions here? (I will need to provide the rest of the sentences)

And for the name, I now have "WebGL OES_texture_float extension". I'm assuming you would rather like "OES_texture_float WebGL extension"?

[ddbeck]

Yeah, I think that looks good.

I'm assuming you would rather like "OES_texture_float WebGL extension"?

Yes, please! Though I imagine "OES_texture_float" or "EXT_color_buffer_half_float" is sufficiently unique by itself.

To embellish on the descriptions a little, I'd write the template like this:

The EXT_[var] extension to WebGL [verbs] [nouns]…

This would also be fine:

The EXT_[var] WebGL extension [verbs] [nouns]…

Though I expect that's a best case scenario. I won't be bothered to see some "extension represents a…" or "is a…". The audience for this is pretty niche and I won't lose sleep over some basic descriptions, if it's obvious when someone who doesn't know anything about WebGL realizes they're not the audience for this information. 😄

[Elchi3]

Thanks Daniel. This is now ready to review and d144915 might help for taking a look at names and descriptions specifically.