dgram: add support for UDP connected sockets

Added the `dgram.connect()` and `dgram.disconnect()` methods that
associate/disassociate a udp socket to/from a remote address.
It optimizes for cases where lots of packets are sent to the same
address.
Also added the `dgram.remoteAddress()` method to retrieve the associated
remote address.

PR-URL: https://github.com/nodejs/node/pull/26871


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>