dns: improve setServers() errors and performance

Issue 1: make invalid setServers yield uniform error

Behavior:
dns.setServers throws a null pointer dereference on some inputs.
Expected behavior was the more pleasant
  TypeError [ERR_INVALID_IP_ADDRESS] ...

Root cause(s?):
- Dereferencing the result of a regex match without confirming
  that there was a match.
- assuming the capture of an optional group (?)

Solution:
Confirm the match, and handle a missing port cleanly.

Tests: I added tests for various unusual inputs.

Issue 2: revise quadratic regex in setServers

Problem:
The IPv6 regex was quadratic.
On long malicious input the event loop could block.

The security team did not deem it a security risk,
but said a PR was welcome.

Solution:
Revise the regex to a linear-complexity version.

Tests:
I added REDOS tests to the "oddities" section.

Fixes: https://github.com/nodejs/node/issues/20441
Fixes: https://github.com/nodejs/node/issues/20443

PR-URL: https://github.com/nodejs/node/pull/20445


Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>