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.

首先阅读 src/Microsoft.OpenApi/Services/OpenApiComparer.cs，并检查 vnext 分支中的有效实现。确定预期的解决方案是删除该方法、让其抛出异常，还是移植 vnext 的实现；当 OpenApiComparer 不再针对比较静默返回空结果时，即视为完成。