Previously, `1.0.0` was used for the version. This is inconsistent with the versioning used in the other default themes, which use use X.X and not X.X.X.
This change corrects all `1.0.0` occurrences to `1.0`, and adds the additional context of `Twenty Twenty-One` to avoid confusion with `WordPress 1.0`.
Props SergeyBiryukov, poena.
Fixes#51958.
Built from https://develop.svn.wordpress.org/trunk@49826
git-svn-id: http://core.svn.wordpress.org/trunk@49545 1a063a9b-81f0-0310-95a4-ce76da25c4cd