Change arrow pointers to hand pointers on buttons in gallery slideshow

ui/file_manager/gallery/css/gallery.css

 /* Copyright (c) 2014 The Chromium Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file. */
 
 body {
   background-color: black;
   font-size: 84%;
   margin: 0;
   user-select: none;
 }
@@ skipping 1252 matching lines @@
   right: 0;
 }
 
 .gallery[tools][slideshow] .slideshow-toolbar {
   display: flex;
 }
 
 .slideshow-toolbar > div {
   background-position: center;
   background-repeat: no-repeat;
+  cursor: pointer;
   height: 48px;
   opacity: 0.8;
   pointer-events: auto;
   width: 48px;
 }
 
 .slideshow-toolbar > div:hover {
   opacity: 1;
 }
 
@@ skipping 140 matching lines @@
 .thumbnail-view .animation-thumbnail {
   background-repeat: no-repeat;
   background-size: cover;
   display: none;
   position: absolute;
 }
 
 .thumbnail-view .animation-thumbnail.animating {
   display: block;
 }