Add view filter handler for contact reference custom field

If a custom field of type "contact ref"  is added as a filter on a drupal view and exposed to screen, the search doesn't work while we type the name in the input field.

Eg -

• Add a custom field of type contact reference.
• Create a drupal view and add the above field as a filter and expose it to users.
• Search by typing a string on the input field - no results.

It searches by the contact id and not by the display name of the contact.