Feat: Add refreshWidgets() API for dynamic widget list updates [ED-23311]

[Omerisra6]

Summary

Adds a public elementor.refreshWidgets() API that lets third-party code (e.g. Angie) dynamically register new widgets on the server side and then refresh the editor's widget list without a full page reload.

• New PHP AJAX endpoint refresh_widgets_config that returns the complete widget + category configuration (including controls with defaults).
• New JS async refreshWidgets() method on the editor instance that fetches the updated config, replaces widgetsCache, updates panel categories, refreshes the panel route, and reloads the preview iframe.
• Guards the elements panel against missing preset widgets that may no longer exist after a refresh.

Jira

https://elementor.atlassian.net/browse/ED-23311

Usage Example

// 1. Register your widget on the server (e.g. via AJAX or WP hook)
//    — make sure the widget class is registered with Elementor's widget manager.

// 2. From the browser console or your JS code, refresh the editor widget list:
await elementor.refreshWidgets();

// That's it — the panel will show the updated widget list,
// and the preview iframe will reload to pick up new widget assets (CSS/JS).

What happens under the hood

1. An AJAX request fetches the full widget config (title, icon, categories, controls with defaults, etc.) and all panel categories.
2. widgetsCache is cleared and rebuilt with the fresh data.
3. Panel categories are updated.
4. Global CSS is re-rendered.
5. The elementor/widgets/refreshed hook fires (for any listeners).
6. The panel route is refreshed so the Elements tab re-renders.
7. The preview iframe reloads so newly registered widget assets (CSS/JS) are enqueued.

Test plan

• Open the editor, register a new widget server-side (e.g. via mu-plugin or Angie snippet)
• Run await elementor.refreshWidgets() in the browser console
• Verify the new widget appears in the panel under the correct category
• Drag the new widget onto the canvas — verify it renders correctly with default control values
• Verify existing widgets still work normally after the refresh
• Verify no JS errors in console during and after refresh