PR: add codes key/legend for debug output in regex-automata #2172

Job	Run time
testfull-regex	3m 49s
testfull-regex-automata	8m 30s
msrv	54s
test (stable, ubuntu-latest, stable)	3m 39s
test (stable-32, ubuntu-latest, stable, i686-unknown-linux-gnu)	2m 51s
miri-regex-automata	9m 13s
rustfmt	7s
test (stable-powerpc64, ubuntu-latest, stable, powerpc64-unknown-linux-gnu)	7m 33s
testfull-regex-capi	27s
test (stable-s390x, ubuntu-latest, stable, s390x-unknown-linux-gnu)	9m 1s
testfull-regex-syntax	1m 56s
test (beta, ubuntu-latest, beta)	3m 51s
test (nightly, ubuntu-latest, nightly)	3m 50s
test (macos, macos-latest, stable)	8m 59s
test (win-msvc, windows-latest, stable)	7m 9s
test (win-gnu, windows-latest, stable-x86_64-gnu)	3m 35s
	1h 15m 24s

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