Add native yescrypt support

Although we have and use yescrypt in the tree, we currently only use it to provide scrypt (for several formats), but not native yescrypt. For Linux distros that have started to use native yescrypt hashes via libxcrypt (ALT Linux, Kali Linux) and for those that support them (Fedora 29+), these hashes can currently be cracked by using --format=crypt. However, this is suboptimal (memory is getting (de)allocated all the time, which slows things down) and non-portable (the hashes cannot be cracked on a system that doesn't have yescrypt support in its libcrypt). We should add the support into JtR itself, possibly in the same format with scrypt. (A next task then would be also supporting yescrypt ROM.)

Start by reading the existing yescrypt and scrypt implementation and the crypt format handling in John the Ripper. Determine how native yescrypt hashes are represented and how support can avoid relying on the system's libcrypt. Done means native yescrypt hashes can be cracked portably and efficiently, while ROM support remains a separate follow-up.