With this commit the code to evaluate UDQ values has been extended/refactored in
many ways:
- There is an increased awarenwss of variable type, i.e. a well related UDQ
versus a field related UDQ. The variable type flows through the AST, and it
is verified that the expression to evaluate and the target variable are of
compatible types.
- Have added support for UDQ field variables and UDQ group variables.
- The UDQSet type and the UDQDefine::eval() have been refactored to multiplex
on all the UDQ types, and the specialized UDQWellSet has been removed.
