Some auto-complete support for box modules in VSCode and languageserver

### Please describe your feature request

Hi @klmr , I hope you don't mind us using the "feature request" to announce a new `box`-support package.

`{box.lsp}` was just [published](https://cran.r-project.org/web/packages/box.lsp/) on CRAN.

It does not yet have full support of box module auto-completion. The `pkg$function()` and `module$function()` patterns are just too difficult to pull off using external parser hooks. Check the Github [repo](https://github.com/Appsilon/box.lsp) for what works and what doesn't.

Start with the linked box.lsp repository and review its documentation of what currently works and does not work. Investigate how support for the pkg$function() and module$function() auto-completion patterns is handled, and define done as adding the missing support without relying on unspecified parser hooks.

Written by the indexing model from the issue text.