This adds a missing DocBlock for `::register_routes()` and parameter descriptions for `::post_process_item()`. Includes minor documenation fixes in other REST API classes for consistency. Props dkarfa, mukesh27, SergeyBiryukov. Fixes #48841. Built from https://develop.svn.wordpress.org/trunk@47391 git-svn-id: http://core.svn.wordpress.org/trunk@47178 1a063a9b-81f0-0310-95a4-ce76da25c4cd