pcre2grep: Please add support for `--` option delimiter

[alejandro-colomar]

For compatibility with grep(1). I use it in scripts, and recently realized it was giving me errors.

[NWilson]

Of course, feel free to open a PR?

[alejandro-colomar]

Yup, I'll try to find some time.

[carenas]

Yup, I'll try to find some time.

If you need some inspiration, I did it recently for maint/utf8 in fecd1a4
and should be pretty straight forward to adapt IMHO.