Use run-with-idle-timer instead of debounce for responsive image scaling.

Use run-with-idle-timer instead of debounce for responsive image scaling.

* lisp/emacs-lisp/timer.el (debounce, debounce-reduce): Revert macro addition.
https://lists.gnu.org/archive/html/emacs-devel/2019-11/msg01133.html

* lisp/image.el (image-increase-size, image-decrease-size):
Use run-with-idle-timer.
(image--change-size): Rename back from image--change-size-function.

* lisp/image-mode.el (image-mode--setup-mode): Remove hooks
window-size-change-functions and window-selection-change-functions (bug#32672)
(image-fit-to-window): Rename from image--window-change-function.
(image--window-state-change): Rename from image--window-change.
Use run-with-idle-timer.