oclosure.el (oclosure-define): Use `oclosure--copy` to define accessors

oclosure.el (oclosure-define): Use `oclosure--copy` to define accessors

* lisp/emacs-lisp/oclosure.el (oclosure-define): Use `oclosure--copy` to
define accessors.  Fix call to `oclosure--defstruct-make-copiers`.
(oclosure--lambda): New macro extracted from `oclosure-lambda`.
(oclosure-lambda): Use it.
(oclosure--accessor-prototype): New constant.
(oclosure-accessor): New type.