[WIP] PNI - refactored 'focusNextListItem' function

[mmmavis]

Description

Link to sample test page:
Related PRs/issues: #

Checklist

Tests

• Is the code I'm adding covered by tests?

Changes in Models:

• Did I update or add new fake data?
• Did I squash my migration?
• Are my changes backward-compatible. If not, did I schedule a deploy with the rest of the team?

Documentation:

• Is my code documented?
• Did I update the READMEs or wagtail documentation?

Merge Method
💡❗Remember to use squash merge when merging non-feature branches into main

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