`MenuRadioItem`: add an optional checked prefix

[ramonjd]

What?

Add an optional checkedPrefix prop to MenuRadioItem to customize the checked icon.

Why?

The dot may not be desirable in some designs.

How?

Added a checkedPrefix react node prop to the component.

prefix seemed to imply permanence, so I added checked to the front.

Testing Instructions

Fire up story book npm run storybook:dev and preview it here:

http://localhost:50240/?path=/story/components-experimental-menu--with-radios

Testing Instructions for Keyboard

Screenshots or screencast

https://github.com/user-attachments/assets/97cb2e06-a774-431e-be10-5e8834566eea

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Co-authored-by: ramonjd <ramonopoly@git.wordpress.org>
Co-authored-by: jameskoster <jameskoster@git.wordpress.org>

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[jameskoster]

I think the purpose of MenuRadioItem and MenuCheckboxItem is to be opinionated about the design and tie the visuals to underlying semantics. The dot communicates single-select while the check indicates multi-select or toggle-ability. Radios probably shouldn't display checkmarks else we introduce inconsistencies and confusion.

This may have been my fault by sharing a misleading design in https://github.com/WordPress/gutenberg/pull/65619. Apologies!

[ramonjd]

Thanks! Worth a shot 😄 I'll close for now until there's a case for it.