* lisp/calc/calc-yank.el (calc-edit-mode): Make it into a proper major mode

* lisp/calc/calc-yank.el (calc-edit-mode): Make it into a proper major mode

Also make `calc-edit-handler` hold a function instead of an expression.

(calc-original-buffer, calc-return-buffer, calc-one-window)
(calc-edit-handler, calc-restore-trail, calc-allow-ret)
(calc-edit-top): Give them a default value.
(calc--edit-mode): New function extracted from old `calc-edit-mode`.
(calc-edit-return, calc-edit-finish): Don't need to test `boundp` any more.
(calc-edit-finish): Allow `calc-edit-handler` to be a function.

(calc-edit, calc-alg-edit):

* lisp/calc/calc-prog.el (calc-edit-user-syntax, calc-user-define-edit):
* lisp/calc/calc-embed.el (calc-embedded-edit):
* lisp/calc/calc-sel.el (calc-edit-selection):
* lisp/calc/calc-store.el (calc-edit-variable):
Use `calc--edit-mode` and make first arg into a function.

* lisp/calc/calc-ext.el (calc-init-extensions): Autoload `calc--edit-mode`
instead of `calc-edit-mode`.