Better handling of closed user tty

[bjorn3]

Basically it seems like if the user tty is closed, we will have to close the pty leader and then manually send SIGHUP to the foreground process group. See also sudo-project/sudo@41978a5, sudo-project/sudo@a2d01a9, sudo-project/sudo@62e4d29, sudo-project/sudo@fb208d3

[squell]

Note: use_pty become the default in sudo near the end of '23 or early '24. Even though Linux distro's had use_pty in their default sudoers file for quite a while, this change upstream by Todd led to some consternation on his repo. These bugfixes feel like they're all a result of that.

I've also once tested GNU's su pty behaviour on some edge cases and found it to behave not that well as well. Writing this PTY code "correctly for all use cases" is surprisingly difficult (even more difficult for ogsudo since it has to support many more platorms than we do). Which is kind of weird considering that the attack it guards against is not of a type that I think most people think about.

Oh, well.