Support 'required' in details.html.twig by adding a marker to the summary title

Problem/Motivation

The details.html.twig element has a variable 'required' that specifies whether it contains required fields. However, setting this variable has no effect on the visual output:

Seven

Claro

Proposed resolution

Support 'required' in details.html.twig by adding a marker to the summary title.

Remaining tasks

1. Write a patch
2. Review
3. Commit

User interface changes

details.html.twig supports 'required' by adding a marker to the summary title.

API changes

None.

Data model changes

None.