'View linked label' operation added to user entity

The user entity access control handler now handles the 'view linked label' operation (see Drupal\user\UserAccessControlHandler::checkAccess()).

The intent of this entity operation is to determine whether a username theme element can be displayed as a link to the user profile. It differs from the 'view' operation in that it disregards whether a user is viewing their username, and in doing so, does not require the user cache context.

For example, the previous expected functionality was:

• All users with the 'access user profiles' permission see any node author name linked to the author's profile
• Any user viewing a node they authored sees the author name linked to their own profile
• All users not in the first two groups see the node author name as static text

Now, the expected functionality is:

• All users with the 'access user profiles' permission see any node author name linked to the author's profile
• All users without the 'access user profiles' permission see the node author name as static text