Support building the expanded notation for forms

[lu-zero]

Form::op can be either a single entry or multiple.
The protocol-binding-template-specific element to explicitly state the protocol method to use (e.g. htv:methodName) has to be present only once since this is the way the op and the method are mapped.

Would be nice to make so the builder is able to take in the op, method mapping and produce the correct output w/out having to repeat the whole form builder. See w3c/wot-binding-templates#194