Improve multiline input for long commands

[h3zh1]

Problem

Long commands can become difficult to read and edit when they must remain on
a single line.

It is common to split a long command across multiple lines, for example:

apt install \
  vim gcc -y

The two lines should be interpreted as a single command:

[]string{"apt", "install", "vim", "gcc", "-y"}

Currently, this behavior is unavailable when backslashes are treated
literally. This makes long commands less convenient to format and edit.

This request is about entering one logical command across multiple editable
lines, rather than automatic visual wrapping caused by the terminal width.

Would it be possible to improve the multiline input experience for this use
case?

I opened this separate issue to make sure my follow-up in #88 is not overlooked.