Split analyzer and code fix projects

[rockfordlhotka]

Right now the analyzer project includes the code fixes. This is a problem, and they should be split into separate projects, yet still combined into a single NuGet package.

[StefanOssendorf]

Why is this a problem?

[rockfordlhotka]

We are suppressing build errors right now, because the analyzer references a codegen assembly, and it shouldn't do that. A while back I took the easy way out and just ignored the errors (really warnings), but the real fix is to refactor the analyzers and their code-fix part into different projects so they are done correctly.

This is all due to changes to how analyzers and code-fix stuff works compared to when it was originally rolled out years ago.