Lexical: Added about button/view

Re-used existing route and moved tinymce help to its own different
route. Added test to cover.
Added new external-content block to support in editor UI.

resources/js/wysiwyg/ui/index.ts

@@ -4,7 +4,7 @@ import {
     getImageToolbarContent,
     getLinkToolbarContent,
     getMainEditorFullToolbar, getTableToolbarContent
-} from "./toolbars";
+} from "./defaults/toolbars";
 import {EditorUIManager} from "./framework/manager";
 import {EditorUiContext} from "./framework/core";
 import {CodeBlockDecorator} from "./decorators/code-block";