Problem/Motivation
Expand the Field UI to switch between two layouts: one column and two column (left/right)
Since this issue depends on #2296423: Implement layout plugin type in core, modules and themes will have the ability to provide new layouts.
Proposed resolution
Add an experimental module named Field Layout.
It enhances Entity Display entities to store a layout, and enhances the Field UI to expose those settings.
Remaining tasks
N/A
User interface changes
Previously the Field UI showed all fields either in a "Content" region, or as "Disabled".
This will remain unchanged by default, additional layouts are opt-in.
There is an details element at the bottom to allow switching between layouts.
API changes
N/A
Data model changes
N/A, field_layout uses third party settings to store the data