Allow the table widget to display field groups as a dedicated column

Problem/Motivation

We currently have the use case, where our customer often only edits a few specific fields on a paragraph. But we still want to allow them to edit the other paragraph fields on the widget as well.

To do this, we want to have a dedicated column for a specified field group, which would be displayed in the widget.

Steps to reproduce

1. Add a new display mode for your desired paragraph type under "/admin/structure/display-modes/form/add".
2. Inside that display mode, add a new field group, using the Field Group → module.
3. Add the desired fields to the field group and save.
4. Go to the content type referencing the paragraph type through a dedicated paragraphs field
5. In the "form_mode" setting, set your newly created display mode.

Expected
A dedicated column for the field group containing the form elements group for each row appears.

Actual
The fields in the field group are being displayed individually.

Proposed resolution

Add support for field_group and display the field group as a dedicated column in the table.

Remaining tasks

User interface changes

API changes

Data model changes