Add GPUSurfaceConfiguration.colorSpace

[kainino0x]

bikeshedding:

• naming of WGPUColorSpace (WGPUPredefinedColorSpace? note we are likely to use it in non-surface places for copyExternalImageToTexture/importExternalTexture)
• capitalization of WGPUColorSpace_SRGB (Srgb? sRGB?)

Fixes #200

[Kangz]

Should we have the surface capabilities reflect the available color spaces?

[kainino0x]

We talked about this in #200 (comment) but it seemed complex in practice and not necessary yet. On the web we currently just support all three formats with all two color spaces, but in native I don't know if all of those combinations are possible, and certainly new color spaces might not be compatible with all formats or vice versa.

[Kangz]

Ack

[kainino0x]

Approve then? :)
(docs updated)

[kainino0x]

filed #366 for both colorspace and tonemapping capabilities

[eliemichel]

So, what happens if we specify a format that is not Srgb but a colorSpace set to Srgb or the other way around? Is this a way to have the implementation apply the colorSpace change when presenting rather than manually specifying it in the fragment shaders? That's nice if it is so, maybe the following doc (which may be wrong the way I phrase it) to clarify:

      - name: color_space
        doc: |
          Color space transform to apply to the presented textures before displaying them on the surface.
          A value of @ref WGPUColorSpace_SRGB means that pixel values are transformed from linear to [`srgb`](https://www.w3.org/TR/css-color-4/#predefined-sRGB).
          A value of @ref WGPUColorSpace_DisplayP3 means that pixel values are transformed from linear to [`display-p3`](https://www.w3.org/TR/css-color-4/#predefined-display-p3).

          The only value that implementations are required to support is @ref WGPUColorSpace_Undefined,
          which may be either "unmanaged" or "sRGB" in native (translates to the default `"srgb"` in Wasm).
          Wasm implementations should support @ref WGPUColorSpace_SRGB and @ref WGPUColorSpace_DisplayP3.

[kainino0x]

@eliemichel The two concepts are orthogonal though they can be used together. Please check out this draft I opened a while ago and provide any feedback you might have on it:
https://github.com/gpuweb/gpuweb/pull/4597/files

[kainino0x]

Closing this PR, I think we are moving color space and tone mapping to Emscripten extensions.