Create option to switch behavior when multiple entities are referenced by one field

@Grevil: I think this shouldn't be too hard. When looping the entities in the fields, it's just an early exit or comparing the values. And the form element is also simple.

Please use the same keys and values as Webform does for example, but leave out the XOR, I don't think it makes a lot of sense here:

@Grevil: I think this will be an easy one. The most important thing here is to have tests in place. Especially to not break the OR (=Any) existing behavior.

I added the form and schema implementation. Tomorrow I will start with the logic.

Done, please review! All tests and newly added tests are green locally! Let's see what Jenkins has to say about them.

I also found a bug in code, not properly handling multiple referenced entities (as there were no tests for that use case before). All fixed now! :)

Great work @Grevil once again :)
Especially nice tests and super important bugfix!

I left some comments for final adjustments.

What about an update-path? That will definitely be needed for existing installations. Or does it fallback to 'or' gracefully if the value is not set? (might be more stable and safer than an update hook).

After merge we should test this carefully in our projects, where this module is used, before we tag a release.

Fixed the remaining adjustments, good call with the update path! It will only fallback gracefully for the form, but not to the fields itself!! THX!

Sorry, took a bit longer than expected, please review once again.

Fine! RTBC! :)

Note #8! Needs manual testing in dev to be 100% sure.

Merged!

Automatically closed - issue fixed for 2 weeks with no activity.