When a restartable `InteractiveProcess` is canceled, stdin is not rendered

[stuhood]

When a test running via test --debug is restarted due to input files changing (and thus subject to #10705 as well), stdin is no longer echoed back to the user, which means that (for example) the input typed into a pdb session isn't rendered.

This is either because when the interactive process is SIGINT'd it doesn't reverse some modifications it made to the TTY, or because pants' modifications to the TTY aren't properly Drop-guarded.