Replace deprecated / non-standard CSS for `speak` and `aural`

[krokodok]

Both speak: never and @media aural are deprecated and/or non-standard. They are exclusively used for font-icons on pseudo elements. We can replace them with the syntax content: "\icon-code" / "", which is widely supported.

Examples of files where this is used:
– …/src/wp-admin/css/common.css
– …/src/wp-admin/css/themes.css

Both speak: never and @media aural are deprecated and/or non-standard. They are exclusively used for font-icons on pseudo elements. We can replace them with the syntax content: "\icon-code" / "", which is widely supported.

Trac ticket: [](https://core.trac.wordpress.org/ticket/63603#ticket)

[krokodok]

If you would suggest keeping speak: never for future support of CSS3 Speech Module, I can modify my PR to remove only @media aural, which hast not been part of the Draft any more for a long time.

[sabernhardt]

Related: #40428

[audrasjb]

Thank you for opening this issue, the proposed implementation looks good to me. As there is a detailed justification for this change and a functional patch, I'm moving this to 6.9, pending further review.

This will need a trac ticket to be considered for merge; are you planning on opening one, @krokodok?

@joedolson Made a mistake in the formatting of my initial post. There was a link to the ticket: https://core.trac.wordpress.org/ticket/63603