Improve RSA test coverage.

MD5/SHA1 and MDC-2 have special-case logic beyond the generic DigestInfo
wrapping. Test that each of these works, including hash and length
mismatches (both input and signature). Also add VerifyRecover tests. It
appears 5824cc29

 added support for
VerifyRecover, but forgot to add the test data.

Reviewed-by: Kurt Roeckx <kurt@roeckx.be>
Reviewed-by: Rich Salz <rsalz@openssl.org>

GH: #1474