Move back core tests from drools-mvel

see

https://github.com/kiegroup/drools/tree/master/drools-mvel/src/test/java/org/drools/mvel/compiler/phreak

https://github.com/kiegroup/drools/blob/master/drools-mvel/src/test/java/org/drools/mvel/compiler/phreak/PhreakJoinNodeTest.java

https://github.com/kiegroup/drools/blob/master/drools-mvel/src/test/java/org/drools/mvel/compiler/beliefsystem/defeasible/DefeasibilityTest.java

AlphaNodeTest, RightTupleIndexHashTableTest, RightTupleIndexHashTableIteratorTest etc are not testing MVEL they happened to use MVEL, and can be replaced by a lambda.

we need to audit all the tests there, make sure we keep things specifically meant to test MVEL itself, and not a test of something else that happened to use MVEL.