Add a comma-separated/list field formatter for multi-value fields.

We should provide a field formatter that allows people to show a multi-value field as a comma separated list of items. In Drupal 7 this was done by using the https://www.drupal.org/project/field_delimiter module.

Leaving this out will be a regression from Drupal 6. In Drupal 6 you could choose to display taxonomy terms on a node as a comma separated list of links. In Drupal 7, the only way to achieve the same thing was to use the taxonomy formatter module.

I would love to see this common-use-case feature restored to backdrop.

MVP: - Allow separating items by a comma , - Apply this new formatter to any multi-valued field - Allow formatting multi-valued fields as HTML lists (e.g. <ul>, <ol>)

Nice to have:

• Allow separating items by any custom delimiter (e.g. ,, ;, -, etc.)
• Allow specifying a different custom delimiter for the last two items (e.g. &)

Backdrop contrib module: backdrop-contrib/textformatter