API Add AbsoluteLink method to RequestHandler

This is a method that is commonly implemented on controllers, but
it really doesn't need to be.

src/Control/RequestHandler.php

@@ -576,6 +576,17 @@ public function Link($action = null)
         return null;
     }
 
+    /**
+     * Get the absolute URL for this controller, including protocol and host.
+     *
+     * @param string $action See {@link Link()}
+     * @return string
+     */
+    public function AbsoluteLink($action = '')
+    {
+        return Director::absoluteURL((string) $this->Link($action));
+    }
+
     /**
      * Redirect to the given URL.
      */