[Feature request] Source Generators

[Marko-Vujnovic]

I propose adding facilities to the Minsk compiler that would allow it to better cater to users and use-cases that could benefit from code generation. The implementation and the external user-facing interface when interacting with the compiler can be inspired by the recent addition to the Roslyn compiler. Enhancing the compiler with such a feature would not only benefit boilerplate-heavy scenarios, where codebases can be made much less susceptible to the fragility arising from alteration or addition of code that's reliant on handwritten boilerplate code, but also indirectly supplement existing/future metaprogramming abilities of the language without adding special syntax to the language just for this purpose.