Unused import tool

[RazvanN]

Hello everyone,

I have started working on [a tool that identifies unused 
imports](https://github.com/RazvanN7/Unused-Import/tree/master). 
It uses dmd as a library.

The purpose is to have a working tool, but also to better 
understand what sort of information the frontend needs to output 
so that such tools are possible.

Up to this point, I managed to make it work with global imports 
(since dmdfe currently does not provide the scope hierarchy). The 
tool does output some false positives because semantic is 
destructive and some things like aliases or enums are substituted 
eagerly and you cannot trace their origin.

I have tested this tool with some dmd sources and have already 
identified [unused 
imports](https://github.com/dlang/dmd/pulls?q=is%3Apr+delete+unused+imports+author%3ARazvanN7+is%3Aopen)·

So, if you have projects with lots of global imports you could 
use it to at least narrow down the list of potential unused 
imports.

The tool is a work in progress, so if you have any ideas for 
improvement feel free to ping me.

Note that the import paths used are from my machine, so you will 
need to update those accordingly to the files imported in your 
project.

RazvanN