Add package information in completions

[lionel-]

Addresses posit-dev/positron#5225

[DavisVaughan]

I think we also need to let the client know we support this
https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#textDocument_completion

Look for labelDetailsSupport there.

It's possible we could be working with a client that doesn't support this, but it is >3 years old now so its probably ok to ignore the client supplied option for now (we should still set the server side one though)

[DavisVaughan]

I agree that we have many ways to see the function parameters, and by far the most useless one is seeing the function parameters in this completion item menu - the parameters are very scrunched together and you can't see their defaults and they are often cut off. Plus, the point of this menu is to pick the function, not supply the arguments, that comes later

I vote for just showing the package name, and doing a little work to strip out parameters here all together, since its probably a non trivial amount of work to compute it and we won't need it anymore.