Support non-sRGB screencasts

[njdom24]

Would be useful for streaming HDR content via Sunshine LizardByte/Sunshine#5025 without the kms capture backend. Especially if it could work with virtual outputs.
Currently looks like Jay targets gamma 2.2 for compatibility with typical clients.

Requires PipeWire 1.5.81.

Reference implementations:

• Plasma
• GNOME 50 (Merged)

[mahkoh]

If someone wants to work on this, i can review it. Jay is already fully equipped to render to the client buffers in any color space. The information just needs the be sent from the portal to the compositor. Then just replace the hardcoded srgb color description by the requested one.