All entity reference fields should add the correct Cache tags

Problem/Motivation

When using, for instance, an Entity Reference select field to Taxonomy terms, the corresponding cache tags needed for clearing the cache when a Taxonomy term changes, are not added.

Steps to reproduce

Make sure the render- and page cache are enabled. Create a webform with a Entity Reference field referencing to a Taxonomy term bundle. Check the webform, when not logged in. Add, remove or change a term. Check the webform again, when not logged in, and see that the Entity Reference field options are not updated.

Proposed resolution

Add the corresponding Cache tags to the element.

Remaining tasks

Add the corresponding Cache tags to the element.

User interface changes

None.

API changes

None?

Data model changes

None.