New upstream LSP features

[alanz]

See https://code.visualstudio.com/updates/v1_19#_language-server-protocol

"The language server protocol was extended with the following new feature: a completion context given access to the trigger character, more completion item and symbol kinds as well as markdown support for completion items and signature help. The protocol additions are available in the 4.0.0-next.x version of the client and server npm modules."

See also haskell/lsp#67