use simple interactive console if stdin is closed (issue 2981)

[obafgkmdh]

This fixes #2981.

[cfbolz]

OK, looks reasonable. Can we write a unit test for this behavior somehow?

[mattip]

It seems CPython forked and created its own version of pyrepl, this was tracked in cpython issue python/cpython#111201. It would be good to try to see what the diff is to that code, and update PyPy to match or at least document the differences.

[mattip]

I wonder if there is some overlap between our pyrepl issues and the ones in cpython https://github.com/python/cpython/labels/topic-repl

[cfbolz]

@mattip yes, I'm following the CPython topic. About half the fixes are for issues in the new features that cpy added, and some are for pyrepl issues.

My strategy would be to wait a few weeks for them to stabilize things and then start to backport fixes (and maybe some of the new features).