Update the collection of JOINs for the existing entities
We create a set of JOINs using the system level JOIN information
for all entities in the report.
If there is already a JOIN for that set of entities then
we'll use the existing specification as there maybe custom options.
Any unused existing JOIN is tested to see if both its entities still exist
and if so we retain it.
[EX-8881] Make sure we keep custom JOINs
Syntax
public void CreateJoins()
