[http-client-csharp] isolating cadl ranch test case projects

[ArcturusZhang]

Now we are putting all the cadl ranch test cases in the same huge project and including all the source code files.
This works fine before the changes of namespaces, but it is not fine after we have the namespace change.
With the namespace, and because of some spec files are shared, we have duplicated generated type with the same name and namespace everywhere (such as in the client structure cases, and in the versioning cases).

One of the solution is that we isolate those test cases into individual test projects.