Bundled Themes: Update Twenty Twenty.

This brings `trunk`'s version of Twenty Twenty in-sync with GitHub.

For a complete list of changes since [46357], see https://github.com/WordPress/twentytwenty/compare/7157870...7246fd6.

Props anlino, ianbelanger, poena, williampatton, nielslange, acosmin, netweb, joyusly, luminuu, itowhid06, cbravobernal, intimez, glauberglauber, ocean90, amolv, briceduclos, aristath, mukesh27, garrett-eclipse, audrasjb, afercia, dianeco, utsav72640, mahesh901122, tobifjellner.
See #48110.
Built from https://develop.svn.wordpress.org/trunk@46445


git-svn-id: https://core.svn.wordpress.org/trunk@46243 1a063a9b-81f0-0310-95a4-ce76da25c4cd