AvaloniaUI
`0xFEFF` (ZWNBSP) is not correctly handled
This is a character commonly found in UTF-16-encoded sources. It is not specifically shown within a box when the option ShowBoxForControlCharacters is enabled.
It looks like AvaloniaEdit is calling Char.IsControl to determine whether the character is a control character.
https://github.com/AvaloniaUI/AvaloniaEdit/blob/master/src/AvaloniaEdit/Rendering/SingleCharacterElementGenerator.cs#L93C42-L93C59
Based on that definition 0xFEFF is not a control character.
VS Code also doesn't treat 0xFEFF as a control character, but it renders it as � (unrecognized character). VS Code highlights the character when Editor > Unicode Highlight: Invisible Characters is enabled.
Looks ShowBoxForControlCharacters is working as intended and a new feature is needed handle those kind of characters.
