WordPress 5.2 adds the `wp_body_open()` function, and the default themes make use of it. This patch adds a shim for `wp_body_open` to bundled themes so this function will also work in older versions of WordPress.
Props lgedeon, johnbillion, timph, ramiy, pento.
Fixes#46679.
Built from https://develop.svn.wordpress.org/trunk@45256
git-svn-id: http://core.svn.wordpress.org/trunk@45065 1a063a9b-81f0-0310-95a4-ce76da25c4cd