Define by-value/reference expectations for action/function payloads.

Descriptions of parameters and return types do not explain expectations for references to Entities.
The metamodel + vocabulary for CSDL allows three types of encodings:
• By-reference, represented as a string containing a URL that references the resource.
• By-reference, represented as an object containing a partial copy of the resource that includes just the @odata.id meta property with a value that is a string containing a URL that references the resource.
• By-value, represented as an object containing a copy of the resource.

For parameters and return-types, the question is which of these are expected in a payload.