Provides more accurate DNS results

This commit adds two new fields: {un,}verified_host_names.

Whereas previously InetAddress was used to resolve reverse domain
names, this instead changes the lookup mechanism to use JNDI allowing
for a deeper view into the DNS. It also accounts for the fact that
multiple PTR records are not forbidden in the DNS specification and are
often used in shared hosting scenarios.

A host name is considered verified if it has a matching forward record.
If a PTR value is found to have multiple A records, it will be
considered verified if any one of the A records matches the original
address. If no matching record is found, it will be reported as an
unverified host name.

Previously, unverified host names were discarded internally by the
InetAddress lookup mechanism and so this data could not be used.

To maintain "bug compatibility" with the previous implementation of the
"host_name" field, which will now be deprecated, the IP address is
returned when a lookup fails.

The host_name field continues to be used, but now will consider all
verified and unverified host names. If finer grained filtering is
needed, then a seperate ticket could be filed for that, but it is
unclear that it is useful enough to justify the work.

Fixes: #18342