MDL-70990 core_editor: Replace EDITOR_CONTENT_RESTORED event

MDL-70990 core_editor: Replace EDITOR_CONTENT_RESTORED event

The legacy M.core.event.EDITOR_CONTENT_RESTORED event has been replaced
with a new core_editor/events::editorContentRestored native DOM event.

The new event can be listened to at any point in the DOM using the
following syntax:

```
import {eventTypes} from 'core_editor/events';

document.addEventListener(eventTypes.editorContentRestored, handler);
```

A backward-compatabibility layer is included to ensure that any legacy
jQuery event is still called with the same arguments.

This legacy bridge will be removed after Moodle 4.3.