MULE-7993 - fixing parse expression checking

Unfortunately the don't. There's no method that can tell if an expression is a parse expression or a single expression. There are some inconsistencies on those methods that we can't change because they affect backward compatibility. Is not that they have bugs, they just validate different things.
Anyway, will try to refactor this code and see if it makes sense to add an isParseExpression method in ExpressionManager so we can reuse this code.