Dispatch the event from the element itself.

So we can use it directly in lit-element templates and don't have to
add an event handler to window etc.

packages/language-select/src/language-select.js

@@ -77,7 +77,7 @@ class LanguageSelect extends LitElement {
                     bubbles: true,
                     detail: {'lang': this.lang},
                 });
-                window.dispatchEvent(event);
+                this.dispatchEvent(event);
 
                 i18n.changeLanguage(this.lang);
             }