Improved support for multiple response types/204 no content

[EventuallyEven]

Given the following definition

"/someurl": {
  "get": {
	"operationId": "someId",
	"tags": ["tag"],
	"parameters": [
	  {
		"name": "thing",
		"in": "path",
		"required": true,
		"schema": {
		  "type": "string"
		}
	  }
	],
	"responses": {
	  "200": {
		"description": "Yes",
		"content": {
		  "application/json": {
			"schema": {
			  "$ref": "someschema"
			}
		  }
		}
	  },
	  "204": {
		"description": "Empty"
	  }
	}
  }
}

we get the following interface method in the api

someId(params: {
        pathParams: { thing: string };
    }): Promise<someschema>;

The ACTUAL values that can be returned are someschema OR a Response object with status 204.
It would be preferable for the api to reflect this, or, even better, if the actual return value was
someschema or void, i.e.

someId(params: {
        pathParams: { thing: string };
    }): Promise<someschema | void>;

[jhannes]

Currently, the following operation will potentially throw an exception:

"/someurl": {
  "get": {
	"operationId": "someId",
	"tags": ["tag"],
	"parameters": [
	  {
		"name": "thing",
		"in": "path",
		"required": true,
		"schema": {
		  "type": "string"
		}
	  }
	],
	"responses": {
	  "200": {
		"description": "Yes",
		"content": {
		  "application/json": {
			"schema": {
			  "$ref": "someschema"
			}
		  }
		}
	  },
	  "400": {
		"description": "An error occurred"
	  }
	}
  }
}```

It may be hard to support the 204 case without making the 400-case worse. What are your thoughts?

[EventuallyEven]

Ideally, error codes would not result in a thrown exception, but a rejecteded promise, regardless of what is declared as possible responses.

Alternatively, maybe any method with JSON as a possible result should result in

someId(params: { <params> }): Promise<someschema | Response>;
This is more correct as handleResponse is
if (contentType && contentType.startsWith("application/json")) { return response.json(); } return response;

[jhannes]

Partially implemented this in 7b8c031