This commits add three endpoints to retrieve and manipulate fonts in WordPress.
This commit also means that we now have a fully functional Font Library in the site editor.
Props get_dave, youknowriad, mmaattiiaass, grantmkin, swissspidy, mcsf, jorbin, ocean90.
See #59166.
Built from https://develop.svn.wordpress.org/trunk@57548
git-svn-id: http://core.svn.wordpress.org/trunk@57049 1a063a9b-81f0-0310-95a4-ce76da25c4cd
