LSP completions do not support additionalTextEdits

[mattmassicotte]

The additionalTextEdits field of CompletionItem is being dropped. The append! completion for Go reproduces this problem.

[mattmassicotte]

This is "addressed" by 634a577. A good fix here would be to expand the ChimeKit completion API, as it cannot currently fully describe what is happening. However, that would be a major effort and not something I can take on right now.