bug#40943: nl: add way to exclude matching lines from getting numbered!

[積丹尼 Dan Jacobson]

(info "(coreutils) nl invocation") says
     ‘pBRE’
          number only lines that contain a match for the basic regular
          expression BRE.  *Note Regular Expressions: (grep)Regular
          Expressions.

OK, but add a new functionality:
     ‘PBRE’
          Do NOT number lines that contain a match for the basic regular
          expression BRE.  *Note Regular Expressions: (grep)Regular
          Expressions.

$ nl --version
nl (GNU coreutils) 8.30