onnxruntime

55f25a4b - Update Attention op to support attention mask for GPT-2 (#4330)

Update Attention op to support attention mask for GPT-2 (#4330) * Support another two format of mask_index input: 2D attention mask, or 1D mask index with end and start positions. * Update dynamic axes of gpt2 with past state * Update script to fuse model with attention mask