LSP code action: remove all unused imported types and values

[lpil]

Discussed in #3241

^{Originally posted by nicklimmm June 3, 2024}
I often find myself removing the unused imported types and values manually after I'm done with prototyping or refactoring.

Gleam can remove all unused imports, but not imported types and values yet.

A simple example:

import gleam/list.{find} // ->`find` is unused
import gleam/uri.{type Uri} // -> `Uri` is unused

Should become:

import gleam/list
import gleam/uri

This would be a good QOL improvement, especially if we are dealing with a lot of imported types and values.