Bundled Themes: Update Twenty Twenty.

* Add a11y-friendly default text-colors when selecting a background-color.
* Remove margins for the group block when a background-color is set.
* Excluding pullquote block from width resize rules.

This brings Twenty Twenty in sync with GitHub. For a full list of changes since [46711], see https://github.com/WordPress/twentytwenty/compare/ab5fa23...162edc0.

Props allancole, karmatosed.
See #48110, #48386, #48450, #48505.
Fixes #48557.
Built from https://develop.svn.wordpress.org/trunk@46713


git-svn-id: https://core.svn.wordpress.org/trunk@46513 1a063a9b-81f0-0310-95a4-ce76da25c4cd