repl: activate previews for lines exceeding the terminal columns

This improves the completion previews by activating them for lines
that exceed the current terminal columns.
As a drive-by fix it also simplifies some statements.

PR-URL: https://github.com/nodejs/node/pull/31112


Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>