Add tests for Annotations/Options refactor

- Add tests for DriverCompatibility.AddImplicitEmitter
- Add tests for DriverCompatibility.AddImplicitOutputFile
- Use a different top name in DriverSpec emit circuit tests for better
  coverage
- Add tests for DriverCompatibility.WriteEmitted
- Add catchWrites firrtlTests utility to intercept file writes
- Add tests for WriteOutputAnnotations
- Add tests for --custom-transforms reversing

Signed-off-by: Schuyler Eldridge <schuyler.eldridge@ibm.com>