title: NSItemProvider loadItem method returns _NSItemProviderSandboxedResource instead of URL
body: <p>In one of the apps I develop, I use a share extension to import Wallet passes (PKPass).</p>
  
  <p>On iOS 13 (including the latest beta 8), when calling the share extension from within the iOS Mail app, the extension is not receiving the data in the expected format (URL). </p>
  
  <p>This is the relevant snippet from the share extension’s ShareViewController:</p>
  
  <pre><code>if let inputItems = self.extensionContext?.inputItems,
     let inputItem = inputItems.first as? NSExtensionItem,
     let attachments = inputItem.attachments,
     let attachment = attachments.first,
     attachment.hasItemConformingToTypeIdentifier("com.apple.pkpass" as String){
      attachment.loadItem(forTypeIdentifier: "com.apple.pkpass" as String, options: nil) { data, error in
          print ("data: \(String(describing: data))")
  }
  </code></pre>
  
  <p>On iOS 12 (latest version) this works fine also for an attachment in the iOS Mail app (in addition e.g. to a file in the Files app); data holds an optional URL.
  The print statement above shows as follows in the console:</p>
  
  <pre><code>data: Optional(file:///var/mobile/Library/Mail/8EF174CF-68B9-414E-A166-D04C9DBE020E/INBOX.imapmbox/Attachments/13846/2/Attachment-1.pkpass)
  </code></pre>
  
  <p>On iOS 13 (beta 8), in the iOS Mail app, data holds an optional _NSItemProviderSandboxedResource.
  The print statement above shows as follows in the console:</p>
  
  <pre><code>data: Optional(&lt;_NSItemProviderSandboxedResource: 0x2839aa9e0&gt;)
  </code></pre>
  
  <p>This seems to affect only the Mail app. In the Files app data holds - as expected - an URL.</p>
  
  <p>Is this a bug (actually I have already reported this using Feedback Assistant back on beta 4) or some new security feature introduced by iOS 13? How can I access the attachment's url/data in this case?</p>