Color management next steps

A lot of things need to happen to enable better color handling throughout the GTK machinery. The basics have landed now. This issue is about tracking the next steps:

• Default color states (srgb, rec2100-pq and their linear variants)
• Wayland color management protocol support
• cicp support
• colorstate handling during texture loading and saving
• yuv support !7542
• Handle colorstates for dmabufs !7542
• Hook up gstreamer media support !7542
• Private GdkColor api
• Private color state apis for rendernodes and snapshot !7537 (closed)
• Hook up css color machinery !7584 (merged)
• Oklab/Oklch support !7801 (merged)
• Interpolation color states for gradients !7584 (merged)
• Better color state / format support in render_texture
• Make GdkColor and related apis public
• Wayland color representation protocol support
• Pango api for stem darkening
• Color states from primaries
• icc support
• HDR metadata !7820 (closed) / !7821
• Tone mapping
• Gamut mapping
• Windows support
• MacOS support
• Do linear compositing by default