Experiment: New DRL Parser : Test failure : Unknown language level

[tkobayas]

Parent issue: #5678

For example, KnowledgeBuilderTest.testWarnOnFunctionReplacementand some other tests fail with

java.lang.RuntimeException: Unknown language level
	at org.drools.drl.parser.DRLFactory.getDRLParser(DRLFactory.java:109)
	at org.drools.drl.parser.DRLFactory.buildParser(DRLFactory.java:71)
	at org.drools.drl.parser.DrlParser.parse(DrlParser.java:87)
	at org.drools.drl.parser.DrlParser.parse(DrlParser.java:93)
	at org.drools.compiler.builder.impl.KnowledgeBuilderImpl.addPackageFromDrl(KnowledgeBuilderImpl.java:314)
	at org.drools.compiler.builder.impl.KnowledgeBuilderImpl.addPackageFromDrl(KnowledgeBuilderImpl.java:300)

It means DrlParser and DRLFactory require more (hopefully clean) integration with the new parser.

[tkobayas]

I'm working in a way that removing DRL10 and introduce a system property drools.drl.antlr4.parser.enabled.

Kind of overlapping #5681

[tkobayas]

Fixed by #5693