Normalize behavior between uploading in the media library and uploading directly to the block editor. Now, when uploading an image with a mime type the server does not support (either in the media library or the block editor), the user will see an error message “This image cannot be processed by the web server. Convert it to JPEG or PNG before uploading”.
Alos, add a new filter `wp_prevent_unsupported_mime_type_uploads` which determines whether the server should prevent uploads for image types it doesn't support. The default value is true and the filter also receives the uploaded image mime type.
Props: joomskys, adamsilverstein, azaozz, swissspidy, joemcgill, flixos90, audrasjb.
Fixes#61167
Built from https://develop.svn.wordpress.org/trunk@60084
git-svn-id: http://core.svn.wordpress.org/trunk@59420 1a063a9b-81f0-0310-95a4-ce76da25c4cd
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