transformers

cfa022e7 - [tests] gpt2 + `CausalLMModelTester` (#41003)

[tests] gpt2 + `CausalLMModelTester` (#41003) * tmp commit * tmp commit * tmp commit * rm old GPT2ModelTester * nit bug * add facilities for encoder-decoder tests; add comments on ALL overwrites/extra fns * vision_encoder_decoder