color-representation: new protocol

This new protocol extension allows clients to specify color
representation metadata. This is orthogonal to color management, which
will be implemented as a separate protocol extension.

This work is based on:

- EGL_EXT_image_dma_buf_import [1], although this specification doesn't
  provide enough guarantees for the purposes of this protocol, and we'd
  need another extension [2].
- VK_KHR_sampler_ycbcr_conversion [3].
- The KMS "COLOR_ENCODING" and "COLOR_RANGE" properties [4].

[1]: https://www.khronos.org/registry/EGL/extensions/EXT/EGL_EXT_image_dma_buf_import.txt
[2]: https://github.com/KhronosGroup/EGL-Registry/issues/173
[3]: https://www.khronos.org/registry/vulkan/specs/1.3-extensions/man/html/VK_KHR_sampler_ycbcr_conversion.html
[4]: https://dri.freedesktop.org/docs/drm/gpu/drm-kms.html#color-management-properties

Signed-off-by: Simon Ser <contact@emersion.fr>
References: wayland/wayland-protocols!14 (comment 805414)
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