Apply the node form meta column pattern to other entity types

Problem/Motivation

In Drupal 7 we introduced a right hand side column (or 'advanced' form group as referred to in core) to the content creation form. The overarching idea was to make a more clear distinction between content items and metadata items. The focus in the main area is on the content fields, additional settings, metadata etc. are less prominently available in the sidebar next to it.

Because this was a impactful change it was deliberately applied to the content creation form only.

But there are more types of things (entities) you can create, like taxonomy terms, media, users(?).

Steps to reproduce

Compare /node/add which has the meta column design to /admin/structure/taxonomy/manage/tags/add and /media/add/document

Proposed resolution

Since the meta-column design pattern on the content form seems to work well, we can consider using it on the creation forms for other entities as well. Thunder's admin theme already offers one way to implement this, which can be seen in thunder_admin.theme

Remaining tasks

• which entities are candidates for this?
• are there new design patterns in there? if so, design for those.
• make the content/metadata separation for each entity type
• discuss whether the meta-column should be available in form display settings (users might abuse it; maybe we should only provide an easy way for modules like Simple XML Sitemap to place their widgets there?)
• sign off on approach and design
• implement in 1 or more patches

User interface changes

yes!

API changes

?

Data model changes

no?

Release notes snippet