[plsql] Support XMLTABLE functions

[adangel]

Oracle allows to execute SQL like queries against a XML document using XMLTABLE and other related functions:
https://docs.oracle.com/en/database/oracle/oracle-database/18/sqlrf/XMLTABLE.html#GUID-C4A32C58-33E5-4CF1-A1FE-039550D3ECFA

Code Sample demonstrating the issue:

SELECT warehouse_name warehouse,
   warehouse2."Water", warehouse2."Rail"
   FROM warehouses,
   XMLTABLE('/Warehouse'
      PASSING warehouses.warehouse_spec
      COLUMNS 
         "Water" varchar2(6) PATH 'WaterAccess',
         "Rail" varchar2(6) PATH 'RailAccess') 
      warehouse2;

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