Views Autocomplete not validating when the autocomplete is not used

Problem/Motivation

Autocompletion is not validating meaning that empty fields can be saved unless users use the autocomplete

Steps to reproduce

Setup an entity reference field to use an autocomplete view as the selection widget and make it required.
Enter a value into the field for an add / edit form. DO NOT select an entry from the list.
Submit the form, see that it saves with an empty value even though it is a required field.

Proposed resolution

Add validation so that we can't save without an entity.

Remaining tasks

Add the validation - The generic selection handler already has this.

User interface changes

N/A

API changes

N/A

Data model changes

N/A