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:

project.scala:
//> using sourceGenerator.scripts ${.}/generator/generator.scala <- This one for specifying the path of the generator
//> using sourceGenerator.excludeScripts true <- to make sure that the generator file is not run from the original scala-cli runner

in your generator file:

generator.scala:
//> using sourceGenerator.inputDirectory "${.}/../source-generator-input" <- Directory where the data file is located
//> using sourceGenerator.glob "glob:test.in" <- Type of files that will be taken to the Bloop Server

[Gedochao]

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

[Gedochao]

@Perklone @bishabosha
Hey, what's the status on this?
As far as I know, this should be unblocked on Bloop's side (cc @tgodzik).
Let me know if you need help.

[Perklone]

Hello, currently there are no update with this atm since I haven't found much time recently, hoping that I can continue sometime soon though.

[bishabosha]

no updates from me either