Create a testing framework for the code generation

[ascott18]

Currently, the code generation has no tests against it other than "run the code generation against Coalesce.Web and Coalesce.Web.Vue and see if they still compile".

There are a few levels of completeness that we can strive for here:

• Level 0: Run the generators to ensure they don't throw exceptions.
• Level 1: Run the generators and then perform string-level verification for expected substrings in the output based on the input that was generated from.
• Level 2: Run generated code through the respective compiler (tsc or Roslyn) to ensure it compiles.
• Level 3: Actually run the code that gets generated to ensure it behaves correctly.

Each level more-or-less builds on the previous level, so it would make sense to start at the beginning and work forwards from there.