Empty fields added to entities in the database when working in multiple languages

[txau]

Replicate:

• blank-state
• add a new language
• add 2 extra fields to the default template "Document" of types text and date
• create an entity, leave the field blank and save
• edit the entity and add a value for the text field and save
• in the database the entity for the other language has an extra property "date" in the metadata with null value

This behavior changes depending on the field types and can affect dozens of fields in big templates. I am not aware of any implications apart from having an inconsistent database.

[LaszloKecskes]

One implication was a migration, that failed a lot and needed to be hot fixed due to data inconsistency issues, this being one of them.

[fnocetti]

I think this is the same scenario as #6510

[LaszloKecskes]

In sprint, since we're handling it together with #6510.