Fix incorrect Swagger return type when using IResult

[martincostello]

PR Title

Fix incorrect Swagger return type when using IResult

PR Description

When a POCO is wrapped in an IResult with minimal actions, an incorrect return type is used to determine the default API response format, which results in the response being mapped incorrectly.

This then results in the metadata specified by an [ProducesResponseType] attribute not being used, resulting in the intended response type not being included in the Swagger documentation.

This change resolves this by using apiResponseType instead of responseType on line 268 as it is in the surrounding code:

aspnetcore/src/Mvc/Mvc.ApiExplorer/src/EndpointMetadataApiDescriptionProvider.cs

Lines 262 to 271 in 5577c0d

	apiResponseType.ModelMetadata = CreateModelMetadata(apiResponseType.Type);
	if (contentTypes.Count > 0)
	{
	AddResponseContentTypes(apiResponseType.ApiResponseFormats, contentTypes);
	}
	else if (CreateDefaultApiResponseFormat(responseType) is { } defaultResponseFormat)
	{
	apiResponseType.ApiResponseFormats.Add(defaultResponseFormat);
	}

I discovered this in a sample project that was using the following code where the ProducesStatusCode() extension methods add an ProducesResponseTypeAttribute to the endpoint metadata:

builder.MapGet("/api/items/{id}", async (
    [FromRoute] Guid id,
    ClaimsPrincipal user,
    ITodoService service,
    CancellationToken cancellationToken) =>
{
    var model = await service.GetAsync(user.GetUserId(), id, cancellationToken);
    return model is null ? Results.NotFound() : Results.Json(model);
})
.ProducesStatusCode(StatusCodes.Status200OK, typeof(TodoItemModel))
.ProducesStatusCode(StatusCodes.Status404NotFound)
.RequireAuthorization();

With the fix this results in the following JSON in the Swagger document:

    "/api/items/{id}": {
      "get": {
        "tags": [
          "TodoApp"
        ],
        "parameters": [
          {
            "name": "id",
            "in": "path",
            "required": true,
            "schema": {
              "type": "string",
              "format": "uuid"
            }
          }
        ],
        "responses": {
          "200": {
            "description": "Success",
            "content": {
              "application/json": {
                "schema": {
                  "$ref": "#/components/schemas/TodoItemModel"
                }
              }
            }
          },
          "404": {
            "description": "Not Found"
          }
        }
      },
    }

Without the change, the JSON is:

    "/api/items/{id}": {
      "get": {
        "tags": [
          "TodoApp"
        ],
        "parameters": [
          {
            "name": "id",
            "in": "path",
            "required": true,
            "schema": {
              "type": "string",
              "format": "uuid"
            }
          }
        ],
        "responses": {
          "200": {
            "description": "Success"
            }
          },
          "404": {
            "description": "Not Found"
          }
        }
      },
    }

[pranavkm]

/azp run

[pranavkm]

Thanks @martincostello!

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[davidfowl]

/azp run

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