Make gAMA and cHRM fallback optional for sRGB #647

Job	Run time
powerpc_cross	8s
rustfmt	6s
feature_check (ubuntu-latest)	59s
build (1.57.0, ubuntu-latest)	1m 3s
feature_check (macos-latest)	31s
test_all (ubuntu-latest)	3m 0s
build (1.57.0, windows-latest)	1m 38s
feature_check (unstable, ubuntu-latest)	1m 0s
test_all (macos-latest)	2m 8s
build (1.57.0, macos-latest)	1m 7s
feature_check (unstable, macos-latest)	37s
build (stable, ubuntu-latest)	12s
feature_check (benchmarks, ubuntu-latest)	1m 3s
build (stable, windows-latest)	55s
feature_check (benchmarks, macos-latest)	31s
build (stable, macos-latest)	11s
build (beta, ubuntu-latest)	12s
build (beta, windows-latest)	39s
build (beta, macos-latest)	17s
build (nightly, ubuntu-latest)	13s
build (nightly, windows-latest)	36s
build (nightly, macos-latest)	18s
	17m 24s

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