filesystems/pjdfstest: new port

pjdfstest is a file system test suite to assess the correctness of file
system implementations in terms of POSIX compliance. This port is for the
Rust rewrite of the sh-based original, which remains in contrib/ for
now.

WWW: https://github.com/saidsay-so/pjdfstest

Reviewed by: olivier
Differential Revision: https://reviews.freebsd.org/D56848