DEV-3190: Add aliasing to allow multiple joins to same table

[mpsolano]

No description provided.

[kulgan]

This is not obvious but its creating two join statements, one for the edge and the other for the destination node. Not clear if both joins will need an alias, but pretty sure the destination node needs one.
I played with this a little bit and was able to get the existing tests to pass

this = self
for e in entities:
  relation = getattr(self.entity(), e)
  alias = aliased(Node.get_subclass_named(relation.target_class.__dst_class__))
  this = self.join(relation.attr[0], relation.attr[1].of_type(alias))

I also had to make an update to self.entity() to cater for when the join_point is an AliasedClass not an entity.