Limit the width of the completer items

[krassowski]

References

Fixes 13 from #495. The idea is that in extreme cases the completer covers the entire window width, which is annoying when someone has two files open side-by-side and looks at the other file, or has the context help open and wants to look at it; in other extreme cases the documentation panels get squished and is not usable.

Code changes

Added CSS only; sadly not scoped to LSP as we cannot modify the completer class easily (needs changes upstream).

User-facing changes

Before:

After:

• when item is not active it is collapsed at 400px with ellipsis indicator
• when item is active the completer gets expanded to a maximum of 600px
• when it is not enough the line breaks and the label gets wrapped on spaces

I do not like the wrapping behaviour too much though (suggestions welcome!).

Backwards-incompatible changes

None

Chores

• linted
• tested
• documented
• changelog entry