Bundled Themes: Fixes JS TypeError in Twenty Twenty.

On mobile devices using a webkit browser, the menu and search modals could not be opened due to a `TypeError: document.body is null`. This commit fixes that issue by adding a `touch-enabled` class to the body for browsers that do not support media queries.

Props quicoto, poena, Boga86, acosmin, macmanx.
Fixes #48601.
Built from https://develop.svn.wordpress.org/trunk@46786


git-svn-id: https://core.svn.wordpress.org/trunk@46586 1a063a9b-81f0-0310-95a4-ce76da25c4cd