FHIR-46548: where clause on alias

[oliveregger]

see FHIR-46548 and zulip thread

group CapabilityStatementRest(source src, target tgt) extends BackboneElement {
  src.resource as s where (src.resource.type != 'CatalogEntry') log(src.resource.type) -> tgt.resource as t then CapabilityStatementRestResource(s, t);

// vs
  src.resource as s where (s.type != 'CatalogEntry') log(s.type) -> tgt.resource as t then CapabilityStatementRestResource(s, t);
}

Brian: Here src.resource is a repeating property. So the rule here is run for each resource.
If I just evaluate this rule without using the alias, it will evaluate based on src which is the parent of the item we're iterating.
Hence this will fail due to either: Performing a != comparison on a collection, the logging in the sample ...