Create differential fuzzers and add them to OSS-Fuzz #2145

Job	Run time
msrv	3m 32s
miri-regex-automata	7m 7s
rustfmt	7s
test (stable, ubuntu-latest, stable)	3m 55s
testfull-regex	3m 52s
test (stable-32, ubuntu-latest, stable, i686-unknown-linux-gnu)	2m 52s
test (stable-powerpc64, ubuntu-latest, stable, powerpc64-unknown-linux-gnu)	7m 27s
testfull-regex-automata	9m 3s
testfull-regex-capi	22s
test (stable-s390x, ubuntu-latest, stable, s390x-unknown-linux-gnu)	9m 27s
test (beta, ubuntu-latest, beta)	3m 43s
test (nightly, ubuntu-latest, nightly)	4m 9s
testfull-regex-syntax	1m 58s
test (macos, macos-latest, stable)	9m 12s
test (win-msvc, windows-latest, stable)	6m 37s
test (win-gnu, windows-latest, stable-x86_64-gnu)	3m 36s
	1h 16m 59s

Provide feedback