See https://chat.fhir.org/#narrow/stream/179266-fhirpath/topic/data.20extraction.20for.20Questionnaires/near/212740081
and https://chat.fhir.org/#narrow/stream/179266-fhirpath/topic/data.20extraction.20for.20Questionnaires/near/212205755

After a long discussion, what seems to have been settled on is the introduction into the FHIR profile of FHIRPath (not the core FHIRPath) of a %factory object (same syntax as %terminologies), that would have functions for creating various types, including Coding, like:

%factory.coding(system, code, display)

This could be used like (per Bryn Rhodes, in that same topic):

ValueSet.expansion.contains.select(Factory.coding(system, code, display))

which would convert the entries under "contains" into Codings.

Also in that thread Grahame Grieve mentioned Quantity, Identifier and Period also other candidates for %factory functions.