Add ONNX export support for huggingface's bigscience/bloom-560m model (#106930)
Port fix from https://github.com/huggingface/safetensors/pull/318 into ONNX exporter until it is merged
* This add support for safetensors to be loaded within a FakeTensorMode, which results in creating `torch.empty((shape,), dtype=)`. This is done through a monkeypatch for the in-progress https://github.com/huggingface/safetensors/pull/318
* Adds a test for the HF bloom model (bigscience/bloom-560m)
* This PR also fixes existing fake tensor unit tests by moving the `torch.onnx.dynamo_export` to be inside the `enable_fake_mode()` context. Although calling `torch.onnx._dynamo_export` works for several models, the right way of using fake mode is calling the exporter within the context manager.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/106930
Approved by: https://github.com/BowenBao
