Ensure `<menu-bar> <edit> <clear>' handles rectangular regions

* lisp/delsel.el (delete-active-region): Autoload it and make it interactive.
* lisp/menu-bar.el (menu-bar-edit-menu): Bind "Clear" to
`delete-active-region'.

etc/NEWS

@@ -298,6 +298,9 @@ prompt, and how you can tweak the file size threshold.
 +++
 ** A prefix arg now causes 'delete-other-frames' to only iconify frames
 
++++
+** The "Edit => Clear" menu item now obeys a rectangular region
+
 +++
 ** New command 'execute-extended-command-for-buffer'.
 This new command, bound to 'M-S-x', works like

lisp/delsel.el

@@ -84,9 +84,11 @@ information on adapting behavior of commands in Delete Selection mode."
 
 (defvar delsel--replace-text-or-position nil)
 
+;;;###autoload
 (defun delete-active-region (&optional killp)
   "Delete the active region.
 If KILLP in not-nil, the active region is killed instead of deleted."
+  (interactive "P")
   (cond
    (killp
     ;; Don't allow `kill-region' to change the value of `this-command'.

lisp/menu-bar.el

@@ -492,7 +492,7 @@
       '(menu-item "Select All" mark-whole-buffer
                   :help "Mark the whole buffer for a subsequent cut/copy"))
     (bindings--define-key menu [clear]
-      '(menu-item "Clear" delete-region
+      '(menu-item "Clear" delete-active-region
                   :enable (and mark-active
                                (not buffer-read-only))
                   :help