Test all possible return types for call-ins and call-outs - testing features added in GT.M V6.3-006

Prior to GTM-8998, GT.M could return only (long or ydb_status_t) as the return value when called as a callin or returning from a callout, and an error was generated if the return value was not 0. Thus any returned/updated values had to be done through the use of IO or just O (output) parameters).

But with GTM-8998, GT.M and YottaDB can return any of the types as return values. We need a new subtest in the xcall test that uses each value type as a return value demonstrating that they work.

This tests the full range of all possible return types for both call-ins and call-outs.