Remove buttons when disabling 'button-mode'

* lisp/button.el (button-mode): Remove all buttons when disabling.
* doc/lispref/display.texi (Button Buffer Commands): Document
the change.  (Bug#73175)

doc/lispref/display.texi

@@ -8053,6 +8053,7 @@ These are commands and functions for locating and operating on
 buttons in an Emacs buffer.
 
 @cindex buffer-button-map
+@findex button-mode
 @code{push-button} is the command that a user uses to actually push
 a button, and is bound by default in the button itself to @key{RET}
 and to @key{mouse-2} using a local keymap in the button's overlay or
@@ -8063,7 +8064,8 @@ additionally available in the keymap stored in
 @code{button-buffer-map} as a parent keymap for its keymap.
 Alternatively, the @code{button-mode} can be switched on for much the
 same effect: It's a minor mode that does nothing else than install
-@code{button-buffer-map} as a minor mode keymap.
+@code{button-buffer-map} as a minor mode keymap (note that disabling
+@code{button-mode} will remove all the buttons in the current buffer).
 
 If the button has a non-@code{nil} @code{follow-link} property, and
 @code{mouse-1-click-follows-link} is set, a quick @key{mouse-1} click

etc/NEWS

@@ -228,6 +228,9 @@ response.
 *** New function 'unbuttonize-region'.
 It removes all the buttons in the specified region.
 
++++
+*** Disabling 'button-mode' now removes all buttons in the current buffer.
+
 ** Eshell
 
 ---

lisp/button.el

@@ -80,8 +80,15 @@ Mode-specific keymaps may want to use this as their parent keymap."
   "<touchscreen-down>" #'push-button)
 
 (define-minor-mode button-mode
-  "A minor mode for navigating to buttons with the TAB key."
-  :keymap button-buffer-map)
+  "A minor mode for navigating to buttons with the TAB key.
+
+Disabling the mode will remove all buttons in the current buffer."
+  :keymap button-buffer-map
+  (when (not button-mode)
+    (save-excursion
+      (save-restriction
+        (widen)
+        (unbuttonize-region (point-min) (point-max))))))
 
 ;; Default properties for buttons.
 (put 'default-button 'face 'button)