Previously, only the active theme was made available. This commit allows for all themes to be queried if the user has the `switch_themes` or `manage_network_themes` capabilities.
This commit also no longer exposes the `page`, `per_page`, `search` and `context` query parameters since they are not supported by this controller.
Props spacedmonkey, lpawlik, TimothyBlynJacobs.
Fixes#50152.
Built from https://develop.svn.wordpress.org/trunk@49925
git-svn-id: http://core.svn.wordpress.org/trunk@49624 1a063a9b-81f0-0310-95a4-ce76da25c4cd