Allow building with c-ares and yet use threaded resolver for the main
host A/AAAA resolving:
`--with-ares` provides the c-ares install path and defaults to use
c-ares for name resolving
`--with-threaded-resolver` still uses c-ares in the build (for HTTPS)
but uses the threaded resolver for "normal" resolves.
It works similarly for cmake: ENABLE_ARES enables ares, and if
ENABLE_THREADED_RESOLVER also is set, c-ares is used for HTTPS RR and
the threaded resolver for "normal" resolves.
HTTPSRR and c-ares-rr are new features return by curl_version_info() and
thus shown by curl -V.
The c-ares-rr feature bit is there to make it possible to distinguish
between builds using c-ares for all name resolves and builds that use
the threaded resolves for the regular name resolves and c-ares for
HTTPSRR only. "c-ares-rr" means it does not use c-ares for "plain" name
resolves.
HTTPSRR support is EXPERIMENTAL only.
Closes#16054
0d4fdbf15d