`WP_Site_Query` provides for a cleaner `prepare_items()` method. It significantly improves the search experience in the sites list table:
* In a subdomain configuration, domain and path are searched for a provided terms.
* In a subdirectory configuration, path is searched for a provided term.
* The full domain is searched in a subdomain configuration rather than the portion not matching the network's domain.
* Terms are searched as `%term%` by default. Adding `*` in the middle of a term will search `%te%rm%`.
Props flixos90, Fab1en.
Fixes#33185, #24833, #21837, #36675.
git-svn-id: https://develop.svn.wordpress.org/trunk@37736 602fd350-edb4-49c9-b593-d223f7449a82
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