`display-p3` color input shorter than `lab` output

[argyleink]

parcel-css repro link

i could see this being marked as "wont fix", but thought you'd be interested to see how many more characters the converted colors to lab are.

[devongovett]

Thanks for the report! I improved it a bit in the above commit so that the original will be preserved. Fallbacks are now generated in levels: Oklab -> Lab -> P3 -> RGB. We start with all levels below and including the authored color space, and remove the ones that aren't compatible with the browser targets.