`escapeshellarg()` is pretty useless on Windows, and there is no way to
support multiple lines (i.e. line breaks). Thus, we use `proc_open()`
instead of `shell_exec()`.
We also remove some apparently superfluous empty lines from the test
expectation; that seems to match libedit behavior on Linux.
Closes GH-9474.
This test won't pass on Windows. The main reason is that the multiline
input is not really possible to create on cmd. But also, because of the
single quotes. And without multiline data piping, it doesn't make sense.
