Fix super_key failed predicate

This is how one of the `selector` subrules looks like in the old parser:

    (DOT super_key)=>DOT { helper.emit($DOT, DroolsEditorType.SYMBOL); } super_key superSuffix

The whole rule is guarded by a syntactic predicate that is used to make
the decision whether this alternative is viable.

Syntactic predicates were removed in ANTLR 4 so this subrule became:

    DOT { helper.emit($DOT, DroolsEditorType.SYMBOL); } super_key superSuffix

The failing predicate is "hidden" inside the `super_key` rule but it actually
cannot be used to make the decision because it is now "invisible". See
https://github.com/antlr/antlr4/blob/master/doc/predicates.md#finding-visible-predicates
that explains how predicates can become invisible. The thing that makes
the predicate invisible here is the action after `DOT`. And since the
alternative is now unguarded it seems viable and so it is taken and
the `super_key` rule is evaluated.

At this point, inside `super_key` there is only a single alternative. It
is guarded by a predicate that evaluates to `false`, which is an error
condition.

The fix is to restore the guard in front of this `selector` alternative
that prevents taking should the super key predicate later turn out to be
false.

Fixes #5703.

drools-drl/drools-drl-parser-tests/src/test/java/org/drools/drl/parser/antlr4/DRLExprParserTest.java

@@ -268,4 +268,23 @@ public void testNestedExpression() throws Exception {
         assertThat(left.getExpression()).isEqualTo("a");
         assertThat(right.getExpression()).isEqualTo("b");
     }
+
+    @Test
+    public void testChainOfMethodCallInConstraint() {
+        String source = "getAddress().getCity().length() == 5";
+        ConstraintConnectiveDescr result = parser.parse( source );
+        assertThat(parser.hasErrors()).as(parser.getErrors().toString()).isFalse();
+
+        assertThat(result.getConnective()).isEqualTo(ConnectiveType.AND);
+        assertThat(result.getDescrs().size()).isEqualTo(1);
+
+        RelationalExprDescr expr = (RelationalExprDescr) result.getDescrs().get( 0 );
+        assertThat(expr.getOperator()).isEqualTo("==");
+
+        AtomicExprDescr left = (AtomicExprDescr) expr.getLeft();
+        AtomicExprDescr right = (AtomicExprDescr) expr.getRight();
+
+        assertThat(left.getExpression()).isEqualTo("getAddress().getCity().length()");
+        assertThat(right.getExpression()).isEqualTo("5");
+    }
 }

drools-drl/drools-drl-parser/src/main/antlr4/org/drools/drl/parser/antlr4/DRL6Expressions.g4

@@ -716,7 +716,7 @@ explicitGenericInvocationSuffix
     ;
 
 selector
-    :   DOT { helper.emit($DOT, DroolsEditorType.SYMBOL); } super_key superSuffix
+    :   { _input.LA(1) == DRLLexer.DOT && helper.validateIdentifierKey(DroolsSoftKeywords.SUPER) }? DOT { helper.emit($DOT, DroolsEditorType.SYMBOL); } super_key superSuffix
     |   DOT { helper.emit($DOT, DroolsEditorType.SYMBOL); } new_key (nonWildcardTypeArguments)? innerCreator
     |   DOT { helper.emit($DOT, DroolsEditorType.SYMBOL); }
                   IDENTIFIER { helper.emit($IDENTIFIER, DroolsEditorType.IDENTIFIER); }