SHA-256 in Firebird 3.0.x

Thanks to contributions from Alex Peshkov and Tony Whyman in Firebird 3.0.4

SHA-256 message digest may be used instead of SHA-1 for generating the client proof:

https://firebirdsql.org/file/documentation/release_notes/html/en/3_0/rnfb30-security-new-authentication.html#rnfb30-security-srp-patch304

Here is the related patch and proposed fix : CORE-5788