Allow explicit creation of interface types from non-abstract classes

[tigloo]

I have a schema that has the following:

• A "Resource" is a basic interface type with properties such as "id", "text", etc.
• Other types such as "Organization", "Patient", "Device" implement "Resource".
• Then there are some types that contain resources, for example a "DiagnosticReport" may have a member "documents: [Resource]".

Due to this I need to expose "Resource" as an interface but also be able to deserialize it as a partial type. I would like to be able to generate a class-based schema using code generation but since Resource needs to be abstract in order to be generated as an interface, I can't deserialize it.