Given the new WordPress browsers support policy, the `screen-reader-text` css
class used in the admin can be updated to use modern CSS and correct syntax. See
https://github.com/wpaccessibility/a11ythemepatterns/blob/master/read-more-links/style.css
Worth noting the `clip` property is deprecated and kept for IE11 and Edge.
- uses `clip-path` for modern browsers
- keeps `clip` for old browsers and update its value to a correct syntax
- resets `clip-path` to `none` where the class is used to dynamically reveal elements
- removes an old rule that made `screen-reader-text` completely invisible in the help tabs `#screen-meta`
- standardizes the rule across CSS files
Fixes#40970.
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