Previously, if a network's domain started with `www.` in a subdomain configuration, a slug lookup with `get_id_from_blogname()` would not match an existing site. A similar lookup in a subdirectory configuration would work fine.
This strips `www.` from the network's domain in a subdomain configuration during the lookup and returns the site as expected.
Adds tests which would previously fail in a subdomain configuration, but now pass in both configurations.
Props igmoweb, flixos90.
Fixes#34450.
git-svn-id: https://develop.svn.wordpress.org/trunk@38658 602fd350-edb4-49c9-b593-d223f7449a82