implement Scroll flash into SelectPanel

[VanAnderson]

Closes https://github.com/github/primer/issues/183

useScrollFlash takes in a ref and implements https://adxlv.computer/projects/flash-scrollers/

The issue implies that this should be a global solution for overlay components, but I think we will want to implement it in the specific use cases of Overlay being used - this is because the scrollable container itself is implemented in the specific use cases of Overlay rather than globally on overlay itself.

Looking at the issue, it seems the primary place where this was needed was SelectPanel, but we can easily put it elsewhere just by using the hook!

Screenshots

Merge checklist

• Added/updated tests
• Added/updated documentation
• Tested in Chrome
• Tested in Firefox
• Tested in Safari
• Tested in Edge

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[smockle]

A couple comments re: code cleanup. I like the overall direction of this—nice idea, making it a hook! ✨

[smockle]

Nice work! LGTM! ✨

[vdepizzol]

This is awesome! 🎉