Done

Also add support for a QUALIFY clause in a query with a GROUP BY. In
this case, the QUALIFY expression may reference aggregate functions.
Previously such queries would give a ClassCastException (trying to
convert a LogicalAggregate to a LogicalProject).

If a QUALIFY expression references or duplicates an expression in the
SELECT clause, we no longer detect and deduplicate that. This has
made one or two plans more verbose. Potentially we would add back
deduplication.

Also converted a few collections from SqlNodeList to List<SqlNode>.
Wrapping the lists as a SqlNode was not buying us much. Added
method `SqlBasicVisitor.visitAll(List<SqlNode>)`.

Close #4061

core/src/main/java/org/apache/calcite/sql/util/SqlVisitor.java

@@ -26,6 +26,8 @@
 import org.apache.calcite.sql.SqlNodeList;
 import org.apache.calcite.sql.SqlOperator;
 
+import java.util.List;
+
 /**
  * Visitor class, follows the
  * {@link org.apache.calcite.util.Glossary#VISITOR_PATTERN visitor pattern}.
@@ -103,4 +105,9 @@ public interface SqlVisitor<R> {
   default R visitNode(SqlNode n) {
     return n.accept(this);
   }
+
+  /** Visits all nodes in a list. */
+  default void visitAll(List<SqlNode> selectList) {
+    selectList.forEach(e -> e.accept(this));
+  }
 }