Correct manual call to after-change-functions

The pre-change-len argument passed to each element of
after-change-fucntions must reflect the length of the affected region
before the change happened.

In Yasnippet's case, the change enacted in yas--snippet-create is the
replacement of a region (which is almost always of length 0) with a
ready-to-navigate snippet template.  The previous implementation
calculated the length of the affected region after that change
happened, which is wrong.

See https://github.com/joaotavora/eglot/issues/462 for a case where
this mattered.

* yasnippet.el (yas--snippet-create): Correct manual call to
after-change-functions.

yasnippet.el

@@ -4188,7 +4188,7 @@ Returns the newly created snippet."
             (yas--snippet-parse-create snippet))
           (run-hook-with-args 'after-change-functions
                               (point-min) (point-max)
-                              (- (point-max) (point-min))))
+                              (- end begin)))
         (when (listp buffer-undo-list)
           (push (cons (point-min) (point-max))
                 buffer-undo-list))