Build refactor

[verytactical]

@byakuren-hijiri: Document and refactor the frontend pipeline. Currently, the way the compiler prepares to calling the precompile function is quite convoluted. All the arguments of the functions used before precompile should be documented, we should extract small methods when possible, and document them, to make that API more useful for third-parties.

@byakuren-hijiri: Extract methods from the build function (src/pipeline/build.ts) to make it more modular. We need to separate the build functionality from CLI parsing and use different methods to create context, compile, and precompile. This is important to implement in order to enable third-party tools to hook into the compilation pipeline in the most flexible way. Perhaps, the best way to achieve this functionality is to create the Builder class with public methods defining the pipeline.

[novusnota]

Great suggestion from the past, and it's already addressed here!

[verytactical]

Thanks, I forgot to link it.