Closes#34044
`EditorMode::SingleLine { auto_width: true }` was only used for the
title editor in the rules library, and following
https://github.com/zed-industries/zed/pull/31994 we can replace that
with a normal single-line editor without problems. The auto-width editor
was interacting badly with the recently-added newline visualization
code, causing a panic during layout---by switching it to
`Editor::single_line` the newline visualization works there too.
Release Notes:
- Fixed a panic that could occur when opening the rules library.
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Co-authored-by: Finn <finn@zed.dev>
3ecdfc9b5a