Consider richer label for Unicode completion

[krobelus]

Kakoune's LSP client, kak-lsp does not fully implement filterText, so when I type \x I get something like this:

so the labels are like \xi however after selecting it, it's properly expanded to ξ.

I think it would be nice if the label would show both \xi as well as ξ. Maybe ξ (\xi). If that is useful in other editors, I'd go for that.

Otherwise it would be nice if you could explicitly set completionItem.filterText = "\xi" and so on. This would allow kak-lsp to add a targeted workaround: if filterText == label && filterText != insertText then kak-lsp could make up a label that is "$filterText ($insertText)".

Kakoune issue for background info: https://github.com/mawww/kakoune/pull/4418

[krobelus]

Otherwise it would be nice if you could explicitly set completionItem.filterText = "\xi" and so on.

Sorry I didn't realize that the absence of filterText already implies that filterText == label, so please disregard that part. In any case I don't think I can add such a workaround without adversely impacting behavior for other servers..