Substitute some customization etc. doc strings

Substitute some customization etc. doc strings

These changes apply substitute-command-keys to some
doc strings that were going through untranslated
when creating customization or other widgets.
* lisp/cus-edit.el (custom-group-value-create):
* lisp/wid-edit.el (widget-default-create):
(widget-push-button-value-create):
Treat the widget tag as a doc string.
* lisp/emacs-lisp/cl-extra.el (cl--describe-class-slot):
Treat the :documentation value as a doc string.
* lisp/wid-edit.el (widget-choose):
Treat the choice names as doc strings.
(widget-default-create): Treat the :doc value as a doc string.
(widget-toggle-value-create): Treat the :on and :off values
as doc strings.
(widget-documentation-string-value-create):
Substitute the doc string.