feat: Remove original file stem from filenames in the blobstorage (#4309)

This way filenames in the blobstorage are just random hex numbers. This also allows us to get rid of
the `sanitize-filename` dependency.

This also requires `Param::Filename` to be set to "debug_logging*.xdc" for messages containing
logging webxdc-s, otherwise they are not detected properly. This is done in "fix:
Message::set_file_from_bytes(): Set Param::Filename", so don't forget to update senders as well.

deltachat-ffi/deltachat.h

@@ -4094,7 +4094,8 @@ char*           dc_msg_get_subject            (const dc_msg_t* msg);
  *
  * Typically files are associated with images, videos, audios, documents.
  * Plain text messages do not have a file.
- * File name may be mangled. To obtain the original attachment filename use dc_msg_get_filename().
+ * The filename isn't meaningful, only the extension is preserved. To obtain the original attachment
+ * filename use dc_msg_get_filename().
  *
  * @memberof dc_msg_t
  * @param msg The message object.