[D8] Add "Required" and "Show by default" option for "Text area with a summary" field/widget

Description of the need

Sometimes you want to force content-editors to provide a summary. Use case would include

• You're showing it in a teaser display mode
• You're using it for the metatag description
• You're using it for search results

The summary input is easy to miss, but is really useful as it avoids needing a second text field for teaser text.

Proposed solution

Implemented for D9^ https://www.drupal.org/project/drupal/issues/1704864 .

Setup options for the "Text area with a summary" widget to allow for the Summary field to be "Shown by default" (instead of collapsed with js) and a field level setting to make the summary value "Required".

Alternatives

This contrib module seems to provide some of these options https://backdropcms.org/project/text_summary_options