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The priority field in an SRV RR indicates a preferential order at which the underlying targets should be utilised. We need to prefer healthy services in order of priority, where 0 is highest. Prior to this commit, we relied on whatever order the dnsclient.getresources method returned. As it turns out, this assumption is incorrect. The order returned is likely whatever order the system resolver received DNS responses in, which may not be ordered according to the spec. This introduces a ResolvedAddress type which holds the priority value for SRV targets, or a stand-in priority of zero for A/AAAA RRs. This type is used as a return value from the underlying name resolution routines in Name and SRVName. In this manner, all ordering by priority and resolved time can be performed directly within the ResolverCache class and calling code can continue to be none-the-wiser. Before sorting, we still ensure that we only consider targets with a priority within the given threshold as previously implemented. See t/115911.