This commit syncs changes for the default theme from its active development repository to core.
This is a follow up to [52081], [52107], [52164], [52222], [52283], [52335], [52375], and [52392].
To view the full set of changes, visit 2ce387178f...8564fd281f.
This changeset also deletes three unused files. These were removed from the dev repo, but never removed from core.
Props richtabor, kjellr.
See #54318.
Built from https://develop.svn.wordpress.org/trunk@52430
git-svn-id: http://core.svn.wordpress.org/trunk@52022 1a063a9b-81f0-0310-95a4-ce76da25c4cd
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