Suggestion: Use CiInterface as completion item kind for typeclasses

[fwcd]

Typeclasses currently use CiClass as completion item kinds. My impression, however, is that most LSP clients (e.g. VSCode) interpret the completion item kind Class to be referring to OOP-style classes, as VSCode's icon suggests:

Since Haskell's typeclasses are semantically much closer to OOP interfaces, my suggestion would be to use CiInterface as completion item kind instead.