Viewing a node with a List field results in fatal error

The fix is easy, let's also write a test.

Started with a test and realized that you can't use field_view_field to render the output, because of #1977464: The custom field which add for comment con't show in views .

So, yeah, #1787238: Convert options module formatters to Plugin system changed the formatter plugin ids from 'list_*' to 'options_list_*'.

The old formatter names came from back when list field types were provided by list.module.
- 'list', being a reserved PHP word, was problematic as a module name in D8 (namespace Drupal\list caused fata errors), and #1592632: Merge List field types into Options module moved those field types, and the associated formatters, to options.module - but didn't change machine names / plugin IDs for any of those, leaving them in the "list_*' namespace.
- Then #1787238: Convert options module formatters to Plugin system added the 'options_' prefix, but:
just on formatters names (not on field types),
without the corresponding updgrade path to account for D7 fields still referencing the old formatter names,
witjout updating the 'default_formatter' property on the field types (which causes the bug seen here)

So there are two ways to envision this:
Either we just revert the formatter names to their old 'list_*' names (followup patch in #1787238-31: Convert options module formatters to Plugin system does that - but doesn't have the nice tests the patch here has). Granted, this leaves plugin names that do not follow the recommended pattern of prefixing with the module name, but this has been the case for almost a year now...
Or we settle on the new 'options_' prefix, but then it's more than fixing the 'default formatter' entry like the patch here does:
- we need to do it for the field types as well,
- we need the corresponding upgrade paths :-)

As per the "quickfix" tag, we probably want to go with the former for now - just fix the critical bug recently introduced by #1787238: Convert options module formatters to Plugin system. Cleaning up the non-standard machine names left by #1592632: Merge List field types into Options module is better be done in a separate task, and was definitely out of scope for #1787238: Convert options module formatters to Plugin system.

Attached patch merges the fix from [##1787238-31] and the tests provided here.

Thanks for merging the patches!

Extended the test coverage and fixed the actual render bug in order to make the test pass.

Committed 1ac72a9 and pushed to 8.x. Thanks!