[SPARK-31906][SQL][DOCS] Enhance comments in NamedExpression.qualifier

### Why are the changes needed?
The qualifier name should contains catalog name.

### Does this PR introduce _any_ user-facing change?
NO.

### How was this patch tested?
UT.

Closes #28726 from lipzhu/SPARK-31906.

Authored-by: lipzhu <lipzhu@ebay.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/namedExpressions.scala

@@ -85,6 +85,7 @@ trait NamedExpression extends Expression {
    *    e.g. top level attributes aliased in the SELECT clause, or column from a LocalRelation.
    * 2. Seq with a Single element: either the table name or the alias name of the table.
    * 3. Seq with 2 elements: database name and table name
+   * 4. Seq with 3 elements: catalog name, database name and table name
    */
   def qualifier: Seq[String]