Can't use Ctrl+C to stop a running command in the built-in shell

For example, the other day I was playing around with [`curl parrot.live`](https://github.com/hugomd/parrot.live) by typing it into the built-in shell. It runs, but Ctrl+C to quit it doesn't work. I haven't found a way to make it do so.

If I'm `mosh`ed into another machine, then I can use Ctrl+C like I would expect. I noticed that in the source for parrot.live, there is a PowerShell script that has the property `TreatControlCAsInput` in it which would seem to disable the shortcut. But that's Windows-specific so I don't think it's the issue in this case.

This was tested with the software keyboard. I haven't tried a Bluetooth one yet.

Possibly related: #738, #813, #862.

Reproduce the problem in the built-in shell with `curl parrot.live`, then compare Ctrl+C behavior with an mosh session. Read the discussion in related issues #738, #813, and #862 to identify the relevant input-handling area. Done means Ctrl+C reliably stops a running command in the built-in shell, including with the software keyboard.

Written by the indexing model from the issue text.