Support cast segment in $expand

In ODATA-32 we added the ability to do things like filtered expands. We also support filtering collections by type using a CAST segment, and should do the same for $expanded properties.

For example;

~Employees/hr.Managers?$expand=DirectReports

today returns only those employees that are managers, and their direct reports.

~Employees?$expand=hr.Managers/DirectReports

today returns all employees and, for those employees that are managers, all of their direct reports.

We would also support:

~Employees/hr.Managers?$expand=DirectReports/hr.Managers

to return only employees that were managers, and only those direct reports that were also managers.

and

~Employees?$expand=hr.Managers/DirectReports/hr.Managers

to return all employees and, for each employee that was a manager, only those direct reports that were also managers.