Attempt to infer better base type than type/* for native queries; fix H2 NPE (#12197)

*  If a driver returns base type `:type/*` (i.e., unknown type) in column metadata for native query results, attempt to infer better type by scanning values sample
*  Fix NPE in H2 native query results for columns where JDBC metadata `.getColumnClassName` returned nil
*  Rename `annotate/column-info*` to `annotate/merged-column-info` (makes the purpose of the function clearer)