Tabs: Don't blur focused tab on sort

Fixes #14627
Closes gh-1761

demos/tabs/sortable.html

@@ -9,10 +9,21 @@
 	<script src="../../external/requirejs/require.js"></script>
 	<script src="../bootstrap.js" data-modules="sortable">
 		var tabs = $( "#tabs" ).tabs();
+		var previouslyFocused = false;
+
 		tabs.find( ".ui-tabs-nav" ).sortable({
 			axis: "x",
-			stop: function() {
+
+			// Sortable removes focus, so we need to restore it if the tab was focused
+			// prior to sorting
+			start: function(event, ui) {
+				previouslyFocused = document.activeElement === ui.item[ 0 ];
+			},
+			stop: function(event, ui) {
 				tabs.tabs( "refresh" );
+				if (previouslyFocused) {
+					ui.item.focus();
+				}
 			}
 		});
 	</script>