Publish our fake TTY implementation as its own package

[novemberborn]

AVA 3 no longer fakes a TTY in worker processes.

Instead we'd like users who depend on a fake TTY to load a helper module. Unfortunately this module does not exist yet.

It should be possible to take the removed code from #2337 and publish it as its own package. Call it fake-tty.

It could have a fake-tty/register entrypoint. This should use some default values for rows and columns.

Once this module exists, we could wrap it in an @ava/fake-tty package which would be able to inherit the settings of the main process through AVA's options. That's not something that regular modules should attempt to access.