xmltable(...) function support

[lovasoa]

Postgres, db2, and oracle all support the xmltable table-valued function.

SELECT xmltable.*
    FROM xmldata,
    XMLTABLE('//ROWS/ROW'
        PASSING data
            COLUMNS id int PATH '@id',
            ordinality FOR ORDINALITY,
            "COUNTRY_NAME" text,
            country_id text PATH 'COUNTRY_ID',
            size_sq_km float PATH 'SIZE[@unit = "sq_km"]',
            size_other text PATH 'concat(SIZE[@unit!="sq_km"], " ", SIZE[@unit!="sq_km"]/@unit)',
            premier_name text PATH 'PREMIER_NAME' DEFAULT 'not specified');

Currently, sqlparser fails to parse it with the following error: Expected: ), found: PASSING

https://www.postgresql.org/docs/15/functions-xml.html#FUNCTIONS-XML-PROCESSING

https://docs.oracle.com/en/database/oracle/oracle-database/19/sqlrf/XMLTABLE.html

https://www.ibm.com/docs/en/db2/12.1.0?topic=data-xmltable-function

Initially reported in sqlpage/SQLPage#887