Media: Prevent uploading and show an error message when the server doesn't support editing of WebP files and image sub-sizes cannot be created.

Props adamsilverstein, desrosj, azaozz
Fixes #53475

git-svn-id: https://develop.svn.wordpress.org/trunk@51211 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/functions.php

@@ -3300,6 +3300,13 @@ function get_allowed_mime_types( $user = null ) {
 		unset( $t['htm|html'], $t['js'] );
 	}
 
+	// Add WebP if the server supports it.
+	unset( $t['webp'] );
+
+	if ( wp_image_editor_supports( array( 'mime_type' => 'image/webp' ) ) ) {
+		$t['webp'] = 'image/webp';
+	}
+
 	/**
 	 * Filters list of allowed mime types and file extensions.
 	 *