BUG: `data` get's lost when processed thru `Neos.Fusion.Form:Runtime.RuntimeForm` outside Form content

[mauricenaef]

Is there an existing issue for this?

• [X] I have searched the existing issues

Current Behavior

When data properties are used inside header or footer part of the form, the Neos.Fusion.Form:Runtime.RuntimeForm strips it's values when form is validated / processed.

Expected Behavior

The data should be keept intact if for instance the form has a custom footer button and code which should persist a form validation / reload.

Steps To Reproduce

1. create a form inside Neos.Fusion.Form:Runtime.RuntimeForm
2. add some non empty field validation
3. overwrite its footer content with defined data properties like custom submit button
4. submit empty form on the front end with validation
5. on processing the data properties are lost

Environment

- Flow: 8.3 
- Neos: 8.3
- PHP: 8.1

Anything else?

All data properties passed inside the form content withstand the issue and are working properly.