Add an argument to `wp_mime_type_icon()` to control the file type returned. Following [57638], there are two file formats in the media icons directory. Different systems would pull up different files by default dependent on the order loaded into the cached array, causing intermittent test failures and unpredictable behavior.
Function update allows core usages to always return the `.svg` while maintaining backwards compatibility for any extended usage that expects a `.png`. Follow up to [57638].
Also handles a missed case in media list view.
Props SergeyBiryukov, sabernhardt, joedolson, antpb.
Fixes#31352.
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