CRM-12925 - Search Builder - Allow CRM_Contact_BAO_Query_Hook to influence options

Note: There was previously a patch to Builder::fields() which allowed CRM_Contact_BAO_Query_Hook to influence list of fields. This extends the same technique to Builder::fieldOptions().

I'm not excited about exposing the current data-structures ($apiEntities or $fieldOptions) to other developers, but the change seems expedient.

Aside: This also fixes display of "enum" fields in the search-builder.