Make PredefinedColorSpace follow the convention of parse() and ToCss … #313

Job	Run time
Linux (nightly)	2m 7s
Linux (nightly, --features dummy_match_byte)	2m 8s
Linux (beta)	34s
Linux (beta, --features dummy_match_byte)	32s
Linux (stable)	32s
Linux (stable, --features dummy_match_byte)	34s
Linux (1.63.0)	1m 51s
Linux (1.63.0, --features dummy_match_byte)	1m 54s
Linux (nightly, --features bench)	3m 57s
Linux (nightly, --features bench,dummy_match_byte)	4m 11s
Result	1s
	18m 21s

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