Convert a payload to and from a Concerto-compliant one

[stefanblaginov]

We would like to be able to convert any payload that has an existing Concerto model to a Concerto-compliant one (i.e. containing $class fields etc).

This already exists in an experimental version in a private repo and can be moved to concerto-tools.

[mttrbrts]

@stefanblaginov is this a duplicate of #542 ?

[DS-AdamMilazzo]

I don't think it's quite the same. #542 still requires $class fields where it would be ambiguous without them. I don't know what it means to talk about a "payload that has an existing Concerto model" that's not already "a Concerto-compliant one". Perhaps it means something like "Here's a bare JSON object. I know it doesn't say so, but it's actually a [email protected]. Now go fix it up to make it legal."? An example would help. :-)