The PR looks good as far as it goes. But you've only changed the parser, so I think it would fall over in the sql-to-rel converter and we would not be able to evaluate these queries. We'd need a test in SqlToRelConverterTest and another test in JdbcTest (similar to JdbcTest.testValues) for this to be complete.
We also need a property to enable/disable this feature, since it's not standard SQL. Add a SqlValidatorTest that calls SqlTester.withConformance(SqlConformance.STRICT_2003) and it should fail, and another that calls SqlTester.withConformance(SqlConformance.PRAGMATIC_2003) and should succeed. After you've done that I'll add a CalciteConnectionProperty value that exposes conformance as a connect-string property.