Raise targetSdk 30

[stefan-niedermann]

• Raises targetSdk to 30
  • Implements the necessary <queries /> to the files app since it is not yet merged in the corresponding SSO pull request
• Discards usage of requestLegacyStorage="true"
• Replaces the preview of downloaded files in the attachment picker with a direct access to the native system file picker because

  • MediaStore is only able to access files if

    The files reside in one of the following well-defined media collections: MediaStore.Images, MediaStore.Video, MediaStore.Audio
    (Source)

    ... which is not true for downloaded content.

  • Also the Storage Access Framework is not able to list content from downloads on Android 11+.