Safari only introduced support for alternative text in generated CSS content in version 17.4, released in 2024. This meets the latest two version declared for core browser support. But because `dashicons.css` is commonly required on the front-end for plugins and themes, this support impacts front-end users, and the browser support guidelines for core should not apply in this context.
Follow up to [60885].
Props codex-m, sabernhardt, wildworks, joedolson, desrosj, welcher.
Fixes#64266.
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