fix: prevent filter from overriding WP_AI_SUPPORT preference

[justlevine]

Trac ticket: https://core.trac.wordpress.org/ticket/64706

This PR fixes wp_supports_ai() to early-return if WP_SUPPORTS_AI is false, instead allowing the wp_supports_ai filter to switch the value back on even if the user/host has explicitly disabled it.

Follow up to #11149

Note

This PR is based on #11149.
Relevant diff: f0c1632

Use of AI Tools

Github Copilot Autocomplete on the doc blocks.

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