Show disabled "Add paragraph / section" buttons with tooltip on translations

Problem/Motivation

Paragraphs can (by design) only be added in the original language and be translated in other languages.

The missing "Add" button confuses people. We're running into this again and again, it even happened to experienced Drupal users. So I think the UX should be improved here.

Steps to reproduce

1. Add some paragraphs in a multi-lang Drupal project
2. Create a translation of the parent entity and search for the "Add" Icons
3. Wonder where they are and be confused :)

Proposed resolution

Show "Add" icons disabled when translating and show a tooltip which explains that adding new paragraphs can only be done in the original language.
Otherwise people think the missing "Add" buttons are a bug.

Remaining tasks

User interface changes

API changes

Data model changes