Emoji: Load wp-emoji-loader as an external script module.

[itzmekhokan]

Converts the emoji detection loader from an inline script module (~3KB inlined on every page) to an external wp-emoji-loader script module, per #64259.

• Registers and enqueues wp-emoji-loader via wp_enqueue_script_module() with fetchpriority=low and in_footer=true
• Passes emoji settings through the script_module_data_wp-emoji-loader filter instead of a hand-printed JSON block
• Updates emoji-loader.js to read wp-script-module-data-wp-emoji-loader (legacy wp-emoji-settings fallback retained)
• Keeps window._wpemojiSettings for backward compatibility

Trac ticket: https://core.trac.wordpress.org/ticket/64259

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