Add JSDoc block for getSectionRootClientId in block editor package

[colorful-tones]

What?

Addresses #65213

Why?

Adding documentation to existing block-editor components can help with any of the following:

• encourages knowledge sharing and quicker onboarding for future devs
• supports maintenance and troubleshooting
• mitigates risk

How?

Add JSDocs formatted doc blocks to existing getSectionRootClientId.

Testing Instructions

Testing Instructions for Keyboard

n/a

[github-actions]

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Co-authored-by: getdave <get_dave@git.wordpress.org>
Co-authored-by: Mamaduka <mamaduka@git.wordpress.org>

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[getdave]

I had this on my todo for today but I appreciate you raising this one 👍

A few tweaks to the wording to express the state as I intended it.

[colorful-tones]

Out sick today, and will circle back and get the suggested updates in place. Thanks!

[getdave]

This is a good improvement. Thank you for following up.