validation packs the original questionnaire response

[FikriMilano]

Describe the bug
When you have a repeated group inside a paginated item, then submit the form, you will save the packed version of the questionnaire response, which is wrong. Packed questionnaire response should only be used when accessing the public API of SDK. Outside of that, implementers should only use the unpacked one.

Quoted from @jingtang10 google/android-fhir#1936 (comment)

Additionally, when questionnaire response is returned to the application, repeated groups need to be unpacked again.

packed = nested items are in the answer property of the repeated group
unpacked = nested items are in the item property of the repeated group

Additional Context

• Initially reported in SDK as point b Matching of the correct pair of qItem and qrItem fails for repeated groups google/android-fhir#2655 (comment)

[FikriMilano]

@allan-on @f-odhiambo @pld