Bug Let Clause Does not have access to Source Alias

[vfrank66]

In a shared library likee CDS_Connect_Commons the let clause is evualted before the query aliases are available in scope.

Example.:

define function ActiveMedicationStatement(MedList List<MedicationStatement>):
  MedList M
    let EffectivePeriod: PeriodToInterval(M.effective as FHIR.Period)
    where M.status.value = 'active'
      and (end of EffectivePeriod is null or end of EffectivePeriod after Now())

The interpreter would perform:

MedList M                                    // Creates alias "M"
  let EffectivePeriod: PeriodToInterval(M.effective)  // ❌ "M" not in scope
  where M.status.value = 'active'            // ✅ "M" would be in scope