Apply new focus styles from WordPress 5.3 more broadly. An updated focus style for form inputs, buttons, and link styled as buttons was added in WordPress 5.3; this commit makes other focus styles consistent with those changes so they meet accessibility standards for color contrast.
Props johnbillion, kebbet, joedolson, afercia.
Fixes#51870.
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git-svn-id: http://core.svn.wordpress.org/trunk@57054 1a063a9b-81f0-0310-95a4-ce76da25c4cd
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