combined with logical "or" and mask type 2 will be returned
      :param attn_mask: attention mask of shape "(seq_len, seq_len)",
      mask type 0 :param key_padding_mask: padding mask of shape
      "(batch_size, seq_len)", mask type 1 :param query: query
      embeddings of shape "(batch_size, seq_len, embed_dim)"
  Returns:
     merged mask mask_type: merged mask type (0, 1, or 2)

  Return type:
     merged_mask
