Don't generate completion when cursor is in a comment

## Is your enhancement request related to a problem? Please describe.

Nil language server has recently gained the ability to not publish completion when typing inside a comment. This made me realized it is possible, and I would like to see it in HLS as well :)

## Describe the solution you'd like

Have the LSP publish completions only when the cursor is not in a comment.

## Describe alternatives you've considered

## Additional context