Can't tab through table inside a widget.

[Jakub Ś]

Steps to reproduce

1. Create a widget which allows inserting table inside editable. You can modify simple box.
2. Insert a table inside the widget.
3. Click inside first table cell and press tab

Expected result

Focus is moved to next table cell like in case of table not inserted into widget.

Actual result

Focus is moved to next widget or out of the editor.

Other details (browser, OS, CKEditor version, installed plugins)

[Jakub Ś]

This ticket seems to be related to: #11700, #12235, #12236.