Menu: Make check for click outside of menu a function which can be overridden. Fixes #8929 - Menu needs adjustement for use in Selectmenu

(cherry picked from commit cceb163)

Author: kborchers

ui/jquery.ui.menu.js

@@ -130,7 +130,7 @@ $.widget( "ui.menu", {
 		// Clicks outside of a menu collapse any open menus
 		this._on( this.document, {
 			click: function( event ) {
-				if ( !$( event.target ).closest( ".ui-menu" ).length ) {
+				if ( this._closeOnDocumentClick( event ) ) {
 					this.collapseAll( event );
 				}
 
@@ -497,6 +497,10 @@ $.widget( "ui.menu", {
 				.removeClass( "ui-state-active" );
 	},
 
+	_closeOnDocumentClick: function( event ) {
+		return !$( event.target ).closest( ".ui-menu" ).length;
+	},
+
 	collapse: function( event ) {
 		var newItem = this.active &&
 			this.active.parent().closest( ".ui-menu-item", this.element );