Code actions for removing dead code

[zth]

• For the dead item itself
• Removing all dead items in the current file

Later on it'd be nice to have a command to run that can remove all of the dead code in a project. This might be better to do in reanalyze itself though? Or we can have an action in the editor that uses the editor to apply the edits. That would be easy to do as a first step. Although it'd only work in VSCode at first.

[cristianoc]

Removing types is much more involved, and unclear how to do automatically. E.g. one variant case.