Expand end-to-end tests for usage with CLI flags

[JoshuaKGoldberg]

Overview

End-to-end test coverage for this project is pretty light. There's only one test in the test/tests/ directory. I'd like to see some more cases covered by it.

At the least, the following would be nice:

• CLI --eslint flag usage
• CLI --package flag usage
• CLI --tslint flag usage
• CLI --typescript flag usage

Some sort of cli.txt file should be supported in the tests folders that indicates custom args to use in the end-to-end test. That way tests can specify custom paths to things.