One thing fairly common to the cache groups is a block of code to look to see when the cache was last changed, and if there isn't one, to set it for the current microtime(). It appears in 8 different places in core. This adds a new helper `wp_cache_get_last_changed` to DRY things up a bit.
Since `wp-includes/cache.php` isn't guaranteed to be loaded, this new function is in `wp-includes/functions.php`
Props spacedmonkey, desrosj.
Fixes#37464.
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Previously, `compact()` provided a non existent `$join` and could cause confusion for anyone attempting to extend `WP_Site_Query` with their own tables. This aligns with the current behavior in `WP_Network_Query`.
Props johnjamesjacoby.
Fixes#37922.
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Provides a consistent way to query `$wpdb->blogs` for `WP_Site` objects based on domain, path, site ID, network ID, and more.
Introduces and uses `update_site_cache()` and `_prime_site_caches()` to maintain a cached list of `WP_Site` objects for use in multiple queries.
Props spacedmonkey, flixos90, DrewAPicture, jeremyfelt, ocean90.
See #35791.
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