Add option to generate safe and unsafe conversions for rustified enums #2814

Job	Run time
docs	26s
check-cfg	21s
minimal	18s
quickchecking	20s
msrv	49s
rustfmt-clippy	28s
test-book	12s
test (ubuntu-latest, 9.0, 0, 0, 0, 0)	1m 45s
test-expectations (ubuntu-latest)	21s
test (ubuntu-latest, 9.0, 0, 0, 1, 0)	1m 45s
test (ubuntu-latest, 9.0, 0, 1, 0, 0)	1m 45s
test-no-headers	26s
test (ubuntu-latest, 9.0, 0, 1, 1, 0)	2m 11s
test-expectations (macos-latest)	17s
test (ubuntu-latest, 9.0, 1, 0, 0, 0)	2m 15s
test (ubuntu-latest, 9.0, 1, 0, 1, 0)	2m 17s
test (ubuntu-latest, 9.0, 1, 1, 0, 0)	2m 18s
test (ubuntu-latest, 9.0, 1, 1, 1, 0)	2m 14s
test (ubuntu-latest, 16.0, 0, 0, 0, 0)	4m 6s
test (ubuntu-latest, 16.0, 0, 0, 1, 0)	4m 11s
test (ubuntu-latest, 16.0, 0, 1, 0, 0)	4m 14s
test (ubuntu-latest, 16.0, 0, 1, 1, 0)	4m 18s
test (ubuntu-latest, 16.0, 1, 0, 0, 0)	4m 55s
test (ubuntu-latest, 16.0, 1, 0, 1, 0)	4m 56s
test (ubuntu-latest, 16.0, 1, 1, 0, 0)	5m 16s
test (ubuntu-latest, 16.0, 1, 1, 1, 0)	4m 48s
test (ubuntu-latest, 16.0, 0, 0, 1)	2m 29s
test (macos-latest, 16.0, 0, 0, 0)	2m 0s
success	1s
	1h 1m 42s

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