Add support for open-choice answerFormats in Questionnaire

[fredhersch]

Is your feature request related to a problem? Please describe.
Current SDC library does not support open-choice option

Describe the solution you'd like
Able to provide open-choice as an item type. Specifying this will then implement the behaviour as per the specification

Additional context
Here is a sample Questionnaire that uses open-choice options - https://openhie.github.io/case-reporting-hiv-vn/Questionnaire-hiv-case-report-questionnaire.json.html

There are two scenarios to support:

1. No list to select from:
There are no choices to select from and open-choice just provides a text box and the answer is stored as a String

{ 
"linkId" : "confirming_lab",
 "text" : "Confirming lab", 
"type" : "open-choice", 
"repeats" : false 
},

2. When there is an answerValueSet (or answerOptions) specified
   open-choice renders a selection list (e.g. a drop-down) with an 'other' option which is selected then shows a text box to be populated
   e.g here: there would be a list of occupations and an other option

{ "linkId" : "occupation", 
"text" : "Occupation", 
"type" : "open-choice", 
"repeats" : false, 
"answerValueSet" : "http://openhie.org/fhir/openhie.vn.case-reporting.hiv/ValueSet/vs-hiv-occupation"
 }

Ux designs

For option 1, this should just display a text field

For option 2, this should be a single choice set of options (drop down list or if repeats is true a set of checkboxes with an 'other' option.

• Only 1 option can be selected
• If 'other' is selected, it should enable a text box for completion. Only 1

Here are two designs:

1. The first shows a drop-down list with Other as the option

2. The second is a set of check-boxes with other option

[fredhersch]

@jingtang10 @Tarun-Bhardwaj for triaging

[fredhersch]

Decision to implement as per the current spec:

"Answer is a Coding drawn from a list of possible answers (as with the choice type) or a free-text entry in a string (valueCoding or valueString)."

1. Use autoComplete widget that can allow for free-text entry (if not selected from the list)
2. If option is selected, use valueCoding, if free-text then valueString

Will explore adding a default valueCoding system to the extension and then treating free-text options as valueCoding. @costateixeira to propose to SDC group

cc: @jingtang10, costateixeira