CodeGenerator refactor/rewrite

[JonathanxD]

The intention is to make CodeGenerator more flexible, currently we have 2 types of CodeGenerators, VisitGenerator and ValueGenerator, the second type is useless and only exists because SourceGenerator uses it. I'd like to see an implementation that works like modify.visit, a system like that will be enough to supply all needs.

Note: CodeGenerator should receive the CodePart to process and a Data instance (or a Data instance provided by CodeGenerator.createData() (old makeData)),

CodeGenerator.kt:

interface CodeGenerator<out R> {
  fun process(part: CodePart) = this.process(part, createData())
  fun process(part: CodePart, data: Data): R
  fun createData(): Data
}

VisitorLikeGenerator.kt:

interface VisitorLikeGenerator<out R> : CodeGenerator<R> {
  private val visitors_ = mutableMapOf<Class<*>, Visitor<*>>()

  fun visit(part: CodePart, data: Data) = this.visit(part: CodePart, type: Class<*>, data: Data)
  fun visit(part: CodePart, type: Class<*> data: Data) {
    //...
    visitors.get(type::class.java)!!.visit(part, data, this) //...
    // ...
  }

}
interface Visitor<in P: CodePart> {
  fun visit(codePart: P, data: Data, visitor: VisitorLikeGenerator<*>)
}