ForwardFields Optimizer integration

[skunert]

This PR enables that forwarded fields are considered in the optimizer when they are not forwarded to the same output field.

[rmetzger]

This looks like a syntax error.

[skunert]

Updated to be automatically mergeable.

[StephanEwen]

This is a good feature addition. I think we should address a few points before merging it:

• The old code had the isFieldConstant() method on the optimizer nodes. You are adding more methods for forwarded fields. I think better design is to remove all of those methods and directly supply the SemanticProperties to the (Requested)Global/LocalProperties. The Semantic properties would need a method like getForwardedFields(int input, int field).
• The methods in the (Requested)Global/LocalProperties can then be renamed to filterBySemanticProperties(), rather than filterByNodesConstantSet().
• The LocalProperties have recently been changed to be an immutable type. That is much less error-prone in applications like the optimizer. The getters (for the set of unique fields) should also return immutable types (like Collections.unmodifiableSet(set)). Similar things would be good for the GlobalProperties, RequestedGlobalProperties, and RequestedLocalProperties.
• Given that this is really logic is sensitive and crucial to the correctness of the optimizer, I think we need to have a few dedicated tests for the filterBySemanticProperties() method in the classes GlobalProperties, LocalProperties, RequestedGlobalProperties, and RequestedLocalProperties. There is currently only one test that test end-to-end some properties, but leaves out many cases.