Component: Error-Handling

[StachuDotNet]

This issue is to organize work related to Darklang's error-handling and supporting users' efforts towards preventing, diagnosing, and resolving errors.

General cross-cutting work:

• TODO: fill in

Some specific error reports to consider:

• Got “Unknown error” as a function was throwing an unexpected exception. We hid that exception because we don’t want to show it to grand users, which are not a concern in the CLI
• Got an error “Both values must be the same type” - but which values? That’s not recorded because we assume it’ll be filled in later via traces. But we don’t have traces (and maybe we should, but how)