ensure explicit left side considered for ON clause in join_from

ensure explicit left side considered for ON clause in join_from

Fixed an issue in :meth:`_sql.Select.join_from` where the join condition
between the left and right tables specified in the method call could be
incorrectly determined based on an intermediate table already present in
the FROM clause, rather than matching the foreign keys between the
immediate left and right arguments. The join condition is now determined by
matching primary keys between the two tables explicitly passed to
:meth:`_sql.Select.join_from`, ensuring consistent and predictable join
behavior regardless of the order of join operations or other tables present
in the query.  The fix is applied to both the Core and ORM implementations
of :meth:`_sql.Select.join_from`.

Fixes: #12931
Change-Id: Id457d441ee8a1bd64a002e57a9dcfd6fc56ff15e