address: pairs: new helper for JMAP (and maybe lei)
Per JMAP RFC 8621 sec 4.1.2.3, we should be able to
denote the lack of a phrase/comment corresponding to an
email address with a JSON "null" (or Perl `undef').
[
{ "name": "James Smythe", "email": "james@example.com" },
{ "name": null, "email": "jane@example.com" },
{ "name": "John Smith", "email": "john@example.com" }
]
The new "pairs" method just returns a 2 dimensional array
and the consumer will fill in the field names if necessary
(or not).
lei(1) may use the two dimensional array as-is for JSON output.