Add tests to make sure DER can work together with workspaces

Problem/Motivation

Just like DER, workspaces module overrides EFQ query service. Add tests to make sure DER and workspaces can work together.

Proposed resolution

If workspaces module is installed then swap workspaces EFQ service instead of one provided by core.

Remaining tasks

In \Drupal\dynamic_entity_reference\DynamicEntityReferenceServiceProvider, check if workspaces module is installed or not and then swap workspaces EFQ service instead of one provided by core.
Add tests.

User interface changes

None.

API changes

None

Data model changes

None

Release notes snippet

TBD.