SchemaView should handle shared attributes with shared names appropriately

[cmungall]

classes:
  C:
    attributes:
      a:
         ...
  D:
    attributes:
      a:
          ...

when using methods such as induced_slot that are contextualized by class, the behavior is umabiguous

however, when using the general get_slots method, the behavior can be ambiguous for fetching attribute a. SchemaView should return a slot when attributes=True is passed.