@FunctionalInterface
public interface CompilationUnit.ClassgenCallback A callback interface you can use during the classgen
phase of compilation as the compiler traverses the ClassNode tree.
You will be called-back for each primary and inner class.
Use setClassgenCallback() before running compile() to set your callback.
Called after bytecode has been generated for a class.
writer - the ASM visitor used to emit the classnode - the generated class node