Add support for Bcrypt algorithm version 2y

[docelic]

This is related to #11595 and the suggestion from @Blacksmoke16 to
also add support for version 2y.

As per https://en.wikipedia.org/wiki/Bcrypt, it seems 2y is limited
to hashes generated by the fixed PHP algorithm.

[straight-shoota]

I'm not familiar with bcrypt version support. But I suppose it's fine to add 2y as supported because its implementation is identical to the existing versions.

Why not add 2x as well, though?

[docelic]

As per the linked Wikipedia article, it seems 2x is a non-compatible implementation (one with a bug):

"In June 2011, a bug was discovered in crypt_blowfish, a PHP implementation of bcrypt. It was mis-handling characters with the 8th bit set. They suggested that system administrators update their existing password database, replacing $2a$ with $2x$, to indicate that those hashes are bad (and need to use the old broken algorithm)."