[PP-1] Handle fields with multiple form control elements on the page data form

Overview

✨ Save page data form values in application state with support for undo/redo Active added support for handling fields with a single form control element. This covers the majority of the Article node form (using the Standard installation profile) and the form of the Page entity type (xb_page) provided by the XB module.

We need to support fields where multiple form control elements provide values. Two examples from the forms mentioned above:

1. Article node form: Revision fields (status checkbox + log message text input);
2. Page entity type: Authored on field (date + time inputs).

Proposed resolution

This problem was already solved for component props form. What's different for the page data form is that we don't currently use any kind of schema information similar to component props forms to recognize the situation with form controls relative to fields. We need to come up with a way to do this for the page data form — or any entity form.

Recommended read to understand the problem domain: Experience Builder's Redux-integrated field widgets — 3.3 The spectrum of HTML form control element → component prop flows.