Draft: color: Dummy implementations for color representation and parametric image description

For the Gstreamer draft implementation in gstreamer/gstreamer!6830 (closed)

This is meant as an experiment to explore which functionality we need to implement for initial GstVideoColorimetry support, sending the values needed for the sRGB, bt601, bt709, bt2020-10, bt2100-pq and bt2100-hlq profiles. Values from the client currently only get printed and for now we always use the default sRGB color profile when creating parametric image descriptions.

---

Requires wayland-protocols!183 (https://gitlab.freedesktop.org/rmader/wayland-protocols/-/tree/color-testing for convenience)

Includes !1502