regex: add as_match method to Captures trait #2895

Job	Run time
test (pinned, ubuntu-latest, 1.74.0)	1m 17s
test (stable, ubuntu-latest, stable)	1m 0s
rustfmt	13s
docs	17s
test (beta, ubuntu-latest, beta)	1m 4s
wasm	20s
test (nightly, ubuntu-latest, nightly)	54s
test (stable-musl, ubuntu-latest, stable, x86_64-unknown-linux-musl)	3m 31s
test (stable-x86, ubuntu-latest, stable, i686-unknown-linux-gnu)	1m 26s
test (stable-aarch64, ubuntu-latest, stable, aarch64-unknown-linux-gnu)	3m 21s
test (stable-arm-gnueabihf, ubuntu-latest, stable, armv7-unknown-linux-gnueabihf)	3m 38s
test (stable-arm-musleabihf, ubuntu-latest, stable, armv7-unknown-linux-musleabihf)	4m 10s
test (stable-arm-musleabi, ubuntu-latest, stable, armv7-unknown-linux-musleabi)	3m 57s
test (stable-powerpc64, ubuntu-latest, stable, powerpc64-unknown-linux-gnu)	3m 4s
test (stable-s390x, ubuntu-latest, stable, s390x-unknown-linux-gnu)	3m 7s
test (macos, macos-latest, nightly)	1m 2s
test (win-msvc, windows-2022, nightly)	2m 11s
test (win-gnu, windows-2022, nightly-x86_64-gnu)	2m 15s
	36m 47s

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