Rename image transform commands to be less confusing

Rename image transform commands to be less confusing

* lisp/image-mode.el
(image-transform-original): Rename from this...
(image-transform-reset-to-original): ...to this.  Make old name
into an obsolete function alias and update all callers.
(image-transform-reset): Rename from this...
(image-transform-reset-to-initial): ...to this.  Make old name
into an obsolete function alias and update all callers.
(Bug#51451)
* doc/emacs/files.texi (Image Mode): Update for above change.