api: Add as_match method #2422

Job	Run time
msrv	59s
rustfmt	8s
test (stable, ubuntu-latest, stable)	3m 49s
miri-regex-automata	14m 4s
test (stable-32, ubuntu-latest, stable, i686-unknown-linux-gnu)	2m 46s
testfull-regex	3m 46s
testfull-regex-automata	9m 0s
test (stable-powerpc64, ubuntu-latest, stable, powerpc64-unknown-linux-gnu)	7m 30s
test (stable-s390x, ubuntu-latest, stable, s390x-unknown-linux-gnu)	9m 9s
testfull-regex-capi	21s
test (beta, ubuntu-latest, beta)	3m 44s
testfull-regex-syntax	2m 0s
test (nightly, ubuntu-latest, nightly)	3m 0s
test (macos, macos-latest, stable)	2m 42s
test (win-msvc, windows-latest, stable)	6m 6s
test (win-gnu, windows-latest, stable-x86_64-gnu)	3m 21s
	1h 12m 25s

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