Add LinkTitleVisibility enum and replace usage of DRUPAL_DISABLED, DRUPAL_OPTIONAL and DRUPAL_REQUIRED

Postponing this on 📌 Introduce and make use of NodePreview enum, to replace node related usage of DRUPAL_DISABLED, DRUPAL_OPTIONAL and DRUPAL_REQUIRED constants Active for enum logic reuse.

Only one thing I'm not sure about in LinkFieldTest, not changing status here.

Just did a close review on the MR changes. Agreed this is RTBC. I resolved a couple of the open threads. Left a micro-nit on 1 open thread, but not worth changing the status over it.

However, do we need a CR here to introduce the new enum?

Thanks,
-Derek

Saving credit for code and reviews.