iAPI: align server-side negation truthiness with client side

[shrivastavanolo]

The Interactivity API supports a negation prefix ! in directive values. However, the server-side negation logic relies on PHP's native boolean casting, which disagrees with JavaScript on two values:

• [] (empty array): falsy in PHP, truthy in JavaScript.
• '0' (string zero): falsy in PHP, truthy in JavaScript.

This causes a mismatch between server and client rendering of the same state, breaking the hydration contract of the Interactivity API.

This fix updates the server-side negation logic in WP_Interactivity_API::evaluate() to use JavaScript-compatible truthiness rules for these two cases, ensuring server and client rendering agree.

Trac ticket: https://core.trac.wordpress.org/ticket/62628

Use of AI Tools

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