Add HostResolverInternalResult conversion for system resolver results

Implemented by factoring out the existing HostResolverSystemTask logic
for conversion for writing to HostResolverCache into a conversion
utility function.

And while touching that logic, fixed it up to better handle the case
where the task is only querying a single address family. Previously the
logic always converted to both A and AAAA results, no matter what was
actually queried, which works out fine as long the task either always
resolves both at the same time, or you consistently resolve just one or
the other. If A and AAAA are both resolved separately by separate tasks,
as may be the case once the Host cache rewrite is complete or maybe even
sooner as part of HEv3 work, could result in conflicting cache entries.
Now the logic will convert to (and cache) results only for the queried
types.

Ideally, we'd just entirely convert HostResolverSystemTask to deal
directly with and return HostResolverInternalResults instead of
AddressList, assisting with the removal of more of the technical debt
that AddressList has become, but too much stuff directly interacts with
HostResolverSystemTask and expects AddressList results.

Change-Id: Ie6a0b76ae916184376f4bc8fb8a0540deb705b08
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6770812
Reviewed-by: Kenichi Ishibashi <bashi@chromium.org>
Commit-Queue: Eric Orth <ericorth@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1498505}