Mechanism to catch FIXMEs in generated code

Jose's tool generates Cadl from from Swagger. It generated with several `// FIXME` comments in the generated code whenever we don't feel confident enough that we got the perfect translation and that the consumer of the generated Cadl should evaluate. Unfortunately, nothing requires these to be addressed and it's quite possible (even likely) that once a consumer has cleared the Cadl squiggles, they will assume they're done.

It would be great if we had a Cadl linter rule that would red squiggle FIXME comments. Alternatively, a `@fixme` decorator might be more Cadl-esque but that would probably involve more effort.