Provide generator abstraction

[jangalinski]

Currently implementers of a generator have to come up with a combination of input criterias, context factories and strategy selection.

Simplify usage by providing generate-function that does all this in one stop.

[jangalinski]

inline fun <INPUT:Any, CONTEXT: KotlinCodeGenerationContext<CONTEXT>, reified STRATEGY: KotlinFileSpecStrategy<CONTEXT, INPUT>> generateFn(
  input: INPUT,
  contextFactory: (INPUT) -> CONTEXT,
) : List<KotlinFileSpec> {
  val context = contextFactory.invoke(input)
  return context.registry.strategies.filter(STRATEGY::class).executeAll(context, input)
}