Expose Regex memory usage info (fixes #943) #2205

Job	Run time
rustfmt	17s
msrv	1m 26s
test (stable, ubuntu-latest, stable)	3m 44s
miri-regex-automata	11m 39s
test (stable-32, ubuntu-latest, stable, i686-unknown-linux-gnu)	2m 51s
testfull-regex	3m 45s
test (stable-powerpc64, ubuntu-latest, stable, powerpc64-unknown-linux-gnu)	8m 36s
testfull-regex-automata	8m 46s
testfull-regex-capi	33s
test (stable-s390x, ubuntu-latest, stable, s390x-unknown-linux-gnu)	9m 48s
testfull-regex-syntax	2m 54s
test (beta, ubuntu-latest, beta)	3m 50s
test (nightly, ubuntu-latest, nightly)	3m 56s
test (macos, macos-latest, stable)	3m 36s
test (win-msvc, windows-latest, stable)	6m 37s
test (win-gnu, windows-latest, stable-x86_64-gnu)	3m 45s
	1h 16m 3s

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