Add scaffolding command to c-sharp service emitter

[markcowl]

Add a scaffolding command that does the following to the c-sharp service emitter package

http-server-csharp-scaffold <directory> <path-to-spec>

• Check for existence of dotnet cli and error out with a helpful message if not present
• Instantiate a new MVC project
• Run tsp compile on the given typespec project, using the emit-scaffolding option and <output-dir>/generated as the output path
• Emit instructions for building and launching the project

est: 3