[new-parser] Backward compatibility issues

[tkobayas]

This issue aggregates known backward compatibility issues between new Antlr4 parser and old Antlr3 parser.

• In the new parser, new is not included in drlIdentifier. For example, new is not used in a package name (of course, it's not allowed in Java).
  • See: [incubator-kie-drools-5818] [new-parser] Parsing fails if a Java keyw… #5958
  • Reason: Antlr4 doesn't have syntactic predicate and the parser chooses drlIdentifier rather than new_key creator in primary rule. So far we haven't found a way to prioritize new_key creator, so excluded new from drlIdentifier
• There is some difference in parser error messages between Antlr4 and Antlr3 (e.g.mismatched input vs no viable alternative). We don't have much to do, and the difference is not important.
  • See: DRLExprParserTest in [incubator-kie-drools-5792] [new-parser] improve drools-drl-parser-tests #5855
• Old parser fails to populate common properties (e.g. startCharacter) in some Descr objects. There is no reason for the new parser to mimic the same failure.
  • See: DescrCommonPropertyTest in [incubator-kie-drools-5792] [new-parser] improve drools-drl-parser-tests #5855