FEATURE: Provide events to initialize backend module JS

[markusguenther]

The backend module vanilla JS was only initialized on DOMContentLoaded event.
When you replace the markup in the backend module you probably need to reinitialze
the vanilla JS components for the menu or drop down for instance.

You can use it like this.

window.dispatchEvent(new CustomEvent("neos:neos:initialize", {
     bubbles: true,
     cancelable: true,
 }));

The change provide the following events:

• neos:neos:initialize
• neos:neos:initialize-modal
• neos:neos:initialize-menu-panel
• neos:neos:initialize-tree
• neos:neos:initialize-expandable-elements
• neos:neos:initialize-drop-down-menus
• neos:neos:initialize-user-management
• neos:neos:initialize-user-menu

[pKallert]

Tested it out locally and works fine 👍