Bundled Themes: Update Twenty Twenty.

This brings Twenty Twenty in sync with GitHub. For a full list of changes since 5.3 RC3, see https://github.com/WordPress/twentytwenty/compare/dea9290...c267289.

Props williampatton, poena, andersnoren.
See #48110, #48386, #48450, #48293.
Fixes #48505.
Built from https://develop.svn.wordpress.org/trunk@46668


git-svn-id: https://core.svn.wordpress.org/trunk@46468 1a063a9b-81f0-0310-95a4-ce76da25c4cd