Social links block: Add Clear button for color option

[shimotmk]

What?

Add a clear button just like the other color controls.
Similer #63580

Why?

Add a clear button for consistency

How?

Added clearable: true

Testing Instructions

1. Open a post or page.
2. Insert a Social links block block.
3. You can see that a clear button has been added to the Icon Color and Icon Background.

Testing Instructions for Keyboard

Screenshots or screencast

Before	After

[github-actions]

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Co-authored-by: shimotmk <shimotomoki@git.wordpress.org>
Co-authored-by: carolinan <poena@git.wordpress.org>

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[carolinan]

Hi @shimotmk is there an open issue related to this change?

[shimotmk]

@carolinan
Thank you. 👍
There are no related issues
I found the problem and submitted a PR.

[Mamaduka]

Thanks, @carolinan! I was about to merge this and then had to hop on a call 🙇

[shimotmk]

Thanks for the review!