Accept annotations in org.python.compiler.ClassFile#addField

Currently `org.python.compiler.ClassFile#addField` does not accept annotations (`org.python.compiler.ProxyCodeHelpers.AnnotationDescr`) as an argument. The underlying `org.objectweb.asm.FieldVisitor` supports annotations however. I added a new overload to `addField` to accept annotations, and pass them on to `FieldVisitor` similar to how they are passed for methods in `ClassFile#addMethod`.