Add filetype support for CUE language
Add filetype support for CUE language

This follows the upstream spec as closely as possible.

See:
- https://cuelang.org
- https://cuelang.org/docs/references/spec/

danr/kakoune,danr/kakoune,Somasis/kakoune,Somasis/kakoune,Somasis/kakoune,occivink/kakoune,occivink/kakoune,occivink/kakoune,alexherbo2/kakoune,alexherbo2/kakoune,danr/kakoune,jkonecny12/kakoune,mawww/kakoune,alexherbo2/kakoune,Somasis/kakoune,occivink/kakoune,casimir/kakoune,casimir/kakoune,jkonecny12/kakoune,jkonecny12/kakoune,danr/kakoune,mawww/kakoune,casimir/kakoune,jkonecny12/kakoune,mawww/kakoune,lenormf/kakoune,lenormf/kakoune,casimir/kakoune,alexherbo2/kakoune,lenormf/kakoune,mawww/kakoune,lenormf/kakoune