Views plugins for Relationship's "Contact A" and "Contact B"

Problem/Motivation

When managing relationships, "Contact A" and "Contact B" are used throughout the CRM admin UI.

When creating a view as a site builder, adding fields for Contact A and Contact B is is not super intuitive ("Multiple field setting" -> "Display all values in the same row" -> "Display 1 value(s) starting from 0/1").

Using "Contacts" as a views filter or relationship is not currently usable.

Steps to reproduce

Proposed resolution

Provide a views field plugin that provides simpler "Contact A" and "Contact B" fields for the site builder to select from when creating/editing a view.

Provide analogous views filter and relationship plugins.

Remaining tasks

User interface changes

API changes

Data model changes