Fix: Missing conversion from json styled variable to CSS variable

[karthikeya-io]

What?

Closes #69477

This PR fixes a block validation error occurring when using preset-based styling, ( for some properties like border-radius), defined with CSS variables in the format var:custom|border-radius|large.

How?

• Fix: Missing conversion from json styled variable to CSS variable

Testing Instructions

1. Open a post or page
2. Open the code editor and add the block with block-radius and CSS variable in the format var:custom|border-radius|large.
   Example

<!-- wp:group {"style":{"border":{"radius":"var:custom|border-radius|large"}},"backgroundColor":"brand-accent-1","layout":{"type":"constrained"}} -->
<div class="wp-block-group has-brand-accent-1-background-color has-background" style="border-radius:var(--wp--custom--border-radius--large)"><!-- wp:paragraph -->
<p>test</p>
<!-- /wp:paragraph --></div>
<!-- /wp:group -->

3. Confirm there's no block validation error

Testing Instructions for Keyboard

Same

Screenshots or screencast

Before	After

[github-actions]

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[github-actions]

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Co-authored-by: carolinan <[email protected]>
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