Resource hints allow browsers to prefetch specific pages or render them in the background to perform DNS lookups or to begin the connection handshake (DNS, TCP, TLS) in the background.
By default, `wp_resource_hints()` prints hints for "s.w.org" (the WordPress.org CDN) and for all scripts and styles which are enqueued from external hosts.
Use the `wp_resource_hints` filter to add custom domains and URLs for `dns-prefetch`, `preconnect`, `prefetch` or `prerender`.
Props voldemortensen, swissspidy.
Fixes#34292.
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