Sortable: Update _contactContainers to use page clientX/Y values

The sortable was using the window position compared with page position to
determine where to drop objects.  this was only a problem for sortables far
enough down to require scrolling.

Fixes #10727
Fixes #5039
Closes gh-1475
Closes gh-1585

ui/widgets/sortable.js

@@ -908,7 +908,7 @@ return $.widget( "ui.sortable", $.ui.mouse, {
 			floating = innermostContainer.floating || this._isFloating( this.currentItem );
 			posProperty = floating ? "left" : "top";
 			sizeProperty = floating ? "width" : "height";
-			axis = floating ? "clientX" : "clientY";
+			axis = floating ? "pageX" : "pageY";
 
 			for ( j = this.items.length - 1; j >= 0; j-- ) {
 				if ( !$.contains( this.containers[ innermostIndex ].element[ 0 ], this.items[ j ].item[ 0 ] ) ) {