Bug 1657582 - Add nsIDNSAddrRecord interface r=necko-reviewers,geckoview-reviewers,snorp,mixedpuppy,dragana

This interface extends nsIDNSRecord and makes the DNS code more extensible
by allowing us to support more record types.
This change does require the consumer to be aware of the type they requested
and to QueryInterface to either nsIDNSAddrRecord for regular IP lookups,
or to nsIDNSByTypeRecord for other kinds of lookups.

Differential Revision: https://phabricator.services.mozilla.com/D86177