Tests do not pass in 8.7+

Our unit tests use a mock-with-original-constructor for EntityField, which is something Drupal can't support BC for.

More specifically, up until 8.7, views/field/EntityField used the "entity.manager" service. After 8.7, it removed this deprecated usage and replaced this constructor argument with "entity_type.manager", adding "entity.repository" and "entity_field.manager" as optional arguments to maintain BC, and internally loading these from the container if they were not passed.

To support this without dropping support for 8.3+, the unit test needs to register its mock of entity.manager under the names "entity.repository" and "entity_field.manager" as well.

Once the minimum version is bumped to 8.7+, remove this workaround and only mock the new services.