Improve prefix arg support in 'ediff-scroll-horizontally'
* lisp/vc/ediff-util.el (ediff-scroll-horizontally): Use 'current-prefix-arg' to pass the value of prefix argument to scrolling commands. (Bug#39353) Copyright-paperwork-exempt: yes
* lisp/vc/ediff-util.el (ediff-scroll-horizontally): Use 'current-prefix-arg' to pass the value of prefix argument to scrolling commands. (Bug#39353) Copyright-paperwork-exempt: yes