Add supports for using Source Generator using Directives

[Perklone]

Address #610. Will be a Draft PR until we can get a conclusion regarding the design of how we want to approach having the source generator

This is a concept PR that I had in mind, also discussed with @bishabosha and @kannupriyakalra aswell.

The idea is that use the source generator via directives that would look something like this:

//> using sourceGenerator "${.}/source-generator-input|glob:test.in|python3 ${.}/source-generator-1.py"

the format for the directive is

//> using sourceGenerator inputDirectory|glob|commandProcessor

[Gedochao]

#3035
in case there's anything we can reuse, kudos to @MaciejG604