Before, if you checked a grouped entity for entity access, Group would always return a Forbidden access result if it could not allow access. This is to ensure that Group keeps its promise that anything which is grouped will never "leak" into the public space unless Group explicitly granted access.
After careful consideration, we want to keep this behavior except for one important change: If neither Group nor any of its submodules support a given operation, Neutral will be returned instead. This should keep module and core maintainers happy when they introduce new operations.
Before
Checking access on a group with a supported operation: Allowed/Forbidden
Checking access on a group with an unsupported operation: Neutral
Checking access on a grouped entity with a supported operation: Allowed/Forbidden
Checking access on a grouped entity with an unsupported operation: Forbidden
After
Checking access on a group with a supported operation: Allowed/Forbidden
Checking access on a group with an unsupported operation: Neutral
Checking access on a grouped entity with a supported operation: Allowed/Forbidden
Checking access on a grouped entity with an unsupported operation: Neutral
API additions
\Drupal\group\Plugin\Group\RelationHandler\AccessControlInterface::supportsOperation($operation, $target)
