Performance of async FHIRPath expressions

[fongsean]

memberOf FHIRPath implementation is currently used in the AusCVDRisk calculator. It requires async FHIRPath evaluation and requests to a terminology server.

There is a need to ensure that the client does not make unnecessary calls to the terminology server. i.e. clicking on a checkbox or adding a new character in the textfields might trigger an API call, which is not ideal.

Ideas:

• Check if the variable already has a result, and therefore skip the API request.