Support viewing the intepreted results of diagnostic queries

[henrymercer]

Currently the VS Code extension supports viewing the raw results of diagnostics queries, but it can't view the interpreted results of diagnostics queries like it can for alert and path alert queries. Located diagnostics queries can likely be displayed similarly to alerts — the only difference is that results may have an associated per-result severity, as opposed to the per-query severity of alert queries. Unlocated diagnostics queries are a little more difficult to display. We may want to take inspiration here from the summary table printed by the CLI.