OpenApiComparer is not implemented

Hello,

My team is using this repository to generate our OpenAPI document, and we started using the OpenApiComparer recently in our project. This method returns a value so we believed it was working until recently when after making a change this still returned an empty list.

After looking at the implementation it's quite clear that this method does nothing but it is documented as being a method that "Compares two OpenApiDocuments and returns a list of differences.".

I believe this method should be removed or should throw instead.

After looking a bit more, there seems to be a valid implementation of this in the vnext branch that was never merged into master.

Bắt đầu bằng cách đọc src/Microsoft.OpenApi/Services/OpenApiComparer.cs và kiểm tra phần triển khai hợp lệ trong branch vnext. Xác định xem hướng giải quyết dự kiến là xóa method, khiến method ném exception, hay đưa phần triển khai của vnext sang; hoàn tất khi OpenApiComparer không còn âm thầm trả về kết quả rỗng cho một phép so sánh.