qc: Add qc_get_field_info

This function returns more detailed information about the fields
of a statement. Supersedes qc_get_affected_fields() that will
be deprecated and removed.

Note that this function now introduced new kind of behaviour; the
returned data belongs to the GWBUF and remains valid for as long as
the GWBUF is alive. That means that unnecessary copying need not
be done.

server/core/query_classifier.c

@@ -197,6 +197,14 @@ char* qc_get_affected_fields(GWBUF* query)
     return classifier->qc_get_affected_fields(query);
 }
 
+void qc_get_field_info(GWBUF* query, const QC_FIELD_INFO** infos, size_t* n_infos)
+{
+    QC_TRACE();
+    ss_dassert(classifier);
+
+    classifier->qc_get_field_info(query, infos, n_infos);
+}
+
 char** qc_get_database_names(GWBUF* query, int* sizep)
 {
     QC_TRACE();