Spinners: Toggle a class instead of show/hide.

Toggling spinners also now uses visibility instead of display, so that the space is always reserved and nothing moves around unexpectedly.

props cdog, MikeHansenMe, valendesigns.
fixes #22839. see #31875, #30725.

Built from https://develop.svn.wordpress.org/trunk@31996


git-svn-id: http://core.svn.wordpress.org/trunk@31975 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/css/media-rtl.css

@@ -274,9 +274,8 @@
 
 .find-box-search .spinner {
 	float: none;
-	right: 110px;
+	right: 105px;
 	position: absolute;
-	top: 2px;
 }
 
 .find-box-search,
@@ -911,8 +910,6 @@ border color while dragging a file over the uploader drop area */
 .wp_attachment_image .spinner,
 .A1B1 .spinner {
 	float: right;
-	padding: 0 0 4px 0;
-	vertical-align: bottom;
 }
 
 .imgedit-menu {