deps: reflect c-ares source tree

c-ares refactored their source tree in 1.17.0 which we did not apply in
our update to 1.17.1. This commit syncs our source with their new
structure for easier maintenance going forward. cares.gyp is updated
accordingly.

Refs: https://github.com/c-ares/c-ares/pull/349
Refs: https://github.com/nodejs/node/pull/36207

PR-URL: https://github.com/nodejs/node/pull/39653


Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>