Issue #1872870 by andypost, naquah: Implement a RoleListController and RoleFormController.

.../modules/user/lib/Drupal/user/Plugin/Core/Entity/Role.php

core/modules/user/lib/Drupal/user/RoleFormController.php

core/modules/user/lib/Drupal/user/RoleListController.php

core/modules/user/lib/Drupal/user/RoleStorageController.php

.../modules/user/lib/Drupal/user/Tests/UserRoleAdminTest.php

core/modules/user/user.admin.inc

core/modules/user/user.module