Refactor: move initials logic out of Persona component and into utility

[c-w]

Pull request checklist

• Addresses an existing issue: #0000
• Include a change request file if publishing
• New feature, bugfix, or enhancement
  • Includes tests
• Documentation update

Description of changes

This pull request moves the initials logic to a utility, thus addressing one of the comments that @dzearing left on #760.

Focus areas to test

This change is just a refactor. No new functionality added. Everything is covered by existing unit tests.

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[c-w]

Putting this on the radar of @cliffkoh.

[cliffkoh]

Looks good, thank you!

[c-w]

Pinging @cliffkoh to hit the merge button before the master branch advances again.