Add `from_str()` for trait Enum #1933

Job	Run time
linux stable (default features)	4m 8s
linux stable (with-bytes)	2m 38s
linux nightly (all features)	3m 43s
linux beta (default features)	3m 47s
Miri test	1m 8s
mega-linter	3m 12s
rustfmt check	1m 20s
windows stable (default features)	5m 38s
Check sync-readme	1m 24s
CI self-check	10s
	27m 8s

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