[PlSql] Support XMLTYPE as a native data type (#3654)

sql/plsql/PlSqlParser.g4

@@ -6885,6 +6885,7 @@ native_datatype_element
     | CLOB
     | NCLOB
     | MLSLABEL
+    | XMLTYPE
     ;
 
 bind_variable

sql/plsql/examples/alter_table.sql

@@ -185,4 +185,7 @@ ALTER TABLE employees
     MODIFY LAST_UPDATE_DATE invisible;
 
 ALTER TABLE employees
-    MODIFY LAST_UPDATE_DATE visible;
+    MODIFY LAST_UPDATE_DATE visible;
+
+ALTER TABLE employees
+    ADD XMLTYPE;

sql/plsql/examples/create_table.sql

@@ -394,6 +394,12 @@ CREATE TABLE print_media_demo
          NESTED TABLE ad_textdocs_ntab STORE AS nt_p2
        )
    TABLESPACE tbs_03;
+
+CREATE TABLE T (
+    id number(9,0) primary key,
+    data xmltype
+);
+
 create TABLE PROCESSED AS (
 select * FROM T_ORDER_PROCESSED f)
        --     WHERE