Higher-level wrappers around GResolver. GSocketConnectable provides an
interface for synchronously or asynchronously iterating multiple
socket addresses, with GNetworkAddress and GNetworkService providing
interfaces based on hostname and SRV record resolution.
Part of #548466.
GResolver provides asynchronous (and synchronous-but-cancellable) APIs
for resolving hostnames, reverse-resolving IP addresses back to
hostnames, and resolving SRV records. Part of #548466.