* lisp/emacs-lisp/macroexp.el: Break cycle with bytecomp/byte-opt

* lisp/emacs-lisp/macroexp.el: Break cycle with bytecomp/byte-opt

The recent change in macroexp triggered a cyclic dependency error
during eager macroexpansion when neither `bytecomp` nor `byte-opt` had
been byte-compiled yet.  This fixes it by moving the offending
function to macroexp.el.

* lisp/emacs-lisp/macroexp.el (macroexp--unfold-lambda): Move from
byte-opt.el and rename.
(macroexp--expand-all): Use it.

* lisp/emacs-lisp/byte-opt.el (byte-compile-unfold-lambda): Move to
macroexp.el.
(byte-compile-inline-expand, byte-optimize-form-code-walker):
* lisp/emacs-lisp/bytecomp.el (byte-compile-form):
Use `macroexp--unfold-lambda` instead.