hir: lift alternations' common suffixes too #2537

Job	Run time
test (stable, ubuntu-latest, stable)	3m 18s
test (stable-32, ubuntu-latest, stable, i686-unknown-linux-gnu)	2m 34s
test (stable-powerpc64, ubuntu-latest, stable, powerpc64-unknown-linux-gnu)	7m 45s
testfull-regex	3m 12s
msrv	1m 27s
test (stable-s390x, ubuntu-latest, stable, s390x-unknown-linux-gnu)	9m 34s
miri-regex-automata	14m 26s
test (beta, ubuntu-latest, beta)	3m 32s
testfull-regex-automata	8m 10s
test (nightly, ubuntu-latest, nightly)	2m 48s
testfull-regex-capi	19s
test (macos, macos-latest, stable)	2m 18s
testfull-regex-syntax	1m 45s
test (win-msvc, windows-latest, stable)	6m 11s
rustfmt	6s
test (win-gnu, windows-latest, stable-x86_64-gnu)	3m 26s
	1h 10m 51s

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