Support for `additionalResponses`

Current TD specification introduced the concept of additionalResponses to model APIs that might return different payloads from the same affordance. The field is used also to model both successful responses and error responses. For example, the Thing Description of a Thing Description Directory contains the following:

"actions": {
        "createThing": {
            "description": "Create a Thing Description",
            "uriVariables": {
                "id": {
                    "@type": "ThingID",
                    "title": "Thing Description ID",
                    "type": "string",
                    "format": "iri-reference"
                }
            },
            "input": {
                "description": "The schema is implied by the content type",
                "type": "object"
            },
            "forms": [
                {
                    "href": "/things/{id}",
                    "htv:methodName": "PUT",
                    "contentType": "application/td+json",
                    "response": {
                        "description": "Success response",
                        "htv:statusCodeValue": 201
                    },
                    "additionalResponses": [
                        {
                            "description": "Invalid serialization or TD",
                            "contentType": "application/problem+json",
                            "htv:statusCodeValue": 400
                        }
                    ]
                }
            ]
        },

• https://github.com/w3c/wot-scripting-api/issues/559
• https://github.com/w3c/wot-scripting-api/issues/560

Start by reviewing the additionalResponses example in this issue and the linked issues 559 and 560. Identify how the Scripting API currently models responses, then define support for additional successful and error responses and verify that the linked requirements are addressed.