[Feature]: Introduce ascii mode

[Piturnah]

Type of Feature

Style and UI

Description

We use ⌄ and › to distinguish between something that is expanded or collapsed. These characters may not be available on a system that is ascii-only.

Solution: introduce an ascii-only mode that displays alternative characters in this case (maybe v and >)?

It should be enabled from the command line, and ideally automatically if it's detected that the terminal does not support unicode.

Also a couple of other non-ascii characters about, for example the minibuffer border