[Libraries] Feedback panel - fix fieldnames setting

[charlottesce]

Brief summary of changes

In the feedback panel for an instrument, the only option in 'Field Name' was 'Across all fields'. This PR changes how the field names for an instrument are fetched so that all of them appear as an option too.

Testing instructions (if applicable)

1. Go to Candidate -> Access Profile -> choose a participant -> choose a timepoint -> choose an instrument
2. Open the feedback panel
3. In Field Name, ensure you can see all the fields of that instrument, and not just 'Across all fields'
4. Repeat for a different instrument to make sure the appropriate field names appear for different instruments

Note

This is a CCNA override - https://github.com/aces/CCNA/pull/5444

[miladheshmati]

The code looks good. Tested successfully on my VM.