Cleanup for server scaffolding

[markcowl]

• Validate messages
  • only print traces and ignore stderr (other than traces) unless there is an error.
  • print download location for dotnet
• Decide whether to clear all generated folders when overwrite is specified or add another option
• Check for dotnet presence in the emitter (print trace with download location and do not format)
• Debug formatting issue and update format command as appropriate
• Emit a diagnostic if use-swaggerui is chosen and no OpenAPI3 spec is available