A `WP_Network` object initially matches a row from `wp_site` and is populated with additional properties used by WordPress core. The first iteration is used to retrieve an existing network based on data passed to the class.
* A network can be retrieved by its ID through `WP_Network::get_instance()`, following in the steps of `WP_Post` and `WP_Comment`.
* A network object can be created or completed by passing initial properties in as a standard object to `new WP_Network()`.
Using these methods, we are now able to populate the global `$current_site` during load via this class.
Props johnjamesjacoby, jeremyfelt, drewapicture, wonderboymusic.
See #31985.
Built from https://develop.svn.wordpress.org/trunk@34097
git-svn-id: http://core.svn.wordpress.org/trunk@34065 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Jeremy Felt