Modify Dap2Service to use UnaryOperation.makeOperation

[dlindhol]

UnaryOperation.makeOperation is currently the single place to define mapping from operation expressions (initially for FDML processing instructions). The DAP2 service interface uses the same operation syntax so we should be able to reuse UnaryOperation.makeOperation.

[RyanJHeld]

I just want to point out that UnaryOperation.makeOperation takes name: String and args: List[String] as input, meaning the expression (a string) has already been parsed into these components. Right now, FdmlParser.parseExpression turns a string expression into a CExpr and FdmlReader.makeOperation opens it up and passes name and args to UnaryOperation.makeOperation.