Clear screen and scroll history

[petros]

This is more of a feature request which I can try via a PR if I can get some confirmation that it makes sense and would be considered:

The clear: true option clears the terminal screen but not it's history. This means that despite cleaning the screen, it's not easy to scroll back to the beginning of the most recent test run. That's because the terminal remembers the whole history since the beginning of the session.

https://github.com/lpil/mix-test.watch/blob/345bf7d0df1bf0b6e6cce18db0ae3a36a306aaaf/lib/mix_test_watch/runner.ex#L32e

One possible approach could be to make it optional so that clear would actually run:

clear && printf '\e[3J'

I am not sure what's the equivalent for printf '\e[3J' using IO.ANSI.