Top-level completions could be better

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

When the cursor is on the top-level, and I issue a completion request. Almost all of the results in the dropdown don't make sense. From what I can tell, the completions include symbols that are available within expressions, which aren't valid on the top-level.

## Describe the solution you'd like

For the top-level completions, I think it'd be best to only have snippets related to declarations. So showing snippets for:

- ~~Pragmas~~
- Imports
- Functions
- Typeclasses
- Instances
- Types

If one of these snippets is picked and the user is filling in the placeholders, the regular completions can kick in again.