Introduce check concept from "Azure/openapi-diff" project

The project Azure/openapi-diff produce following output when two versions of a spec are compared: a list of items (error, warning, info) is computed.

Example:

$ oad compare old/added_path.json new/added_path.json
{
  "id": "1001",
  "code": "NoVersionChange",
  "message": "The versions have not changed.",
  "jsonref": "#",
  "json-path": "#",
  "type": "Info"
}
{
  "id": "1039",
  "code": "AddedOperation",
  "message": "The new version is adding an operation that was not found in the old version.",
  "jsonref": "#/paths/~1api~1Operations/post",
  "json-path": "#/paths/api/Operations/post",
  "type": "Info"
}
{
  "id": "1038",
  "code": "AddedPath",
  "message": "The new version is adding a path that was not found in the old version.",
  "jsonref": "#/paths/~1api~1Paths",
  "json-path": "#/paths/api/Paths",
  "type": "Info"
}

The list of rules that are currently checked can be found in their git repository: docs
I had a look at their test suite in this folder: Swagger

To run their the oad tool against it, I had to perform some changes: https://github.com/Azure/openapi-diff/pull/108
Then I have converted the old Swagger 2.0 format to OpenAPI 3.0.1 format.

Of course, I will share my work.
We can then continue the discussion and see how this could be integrated.

Bắt đầu bằng việc đọc tài liệu Azure/openapi-diff và các test openapi-diff/src/modeler/AutoRest.Swagger.Tests/Resource/Swagger của nó, sau đó so sánh các kiểm tra mà chúng báo cáo với hành vi so sánh hiện tại của dự án này. Issue không nêu tên các tệp cục bộ hoặc một entry point; để hoàn thành sẽ cần thống nhất phạm vi tích hợp và các kiểm tra tương ứng.