Autocompletion for ValueSets

[JPercival]

As a CQL author, I want the editor to suggest valuesets when I'm writing retrieves.

[JPercival]

Also, I want the editor to suggest URLs / Ids for ValueSet definitions at the top based on the content of the current IG.

[JPercival]

https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#textDocument_completion