Add support for serializing real tensor data in after aot minifier (#99834)
The new minifier script looks like this:
```
import torch._dynamo.repro.after_aot
reader = torch._dynamo.repro.after_aot.InputReader(save_dir='/tmp/tmpcsngx39e')
buf0 = reader.storage('e2b39c716c0d4efb9fa57375a3902b9dab666893', 16)
t0 = reader.tensor(buf0, (4,))
args = [t0]
mod = make_fx(Repro(), tracing_mode='real')(*args)
```
The real tensor data is stored in the storages folder of the checkpoint dump directory. If you delete this folder / it is otherwise missing, we will transparently fall back to generating random data like before. The tensors are serialized using content store from #99809, which means each storage is content-addressed and we will automatically deduplicate equivalent data (which is useful if you keep dumping out, e.g., your parameters.) We don't use the tensor serialization capability from content store, instead all of the tensor metadata is stored inline inside the repro script (so that everything is in one file if you lose the checkpointed tensors).
We also add a stable_hash option to content store, where we use a slow SHA-1 sum on the data in CPU side to compute a hash that is stable across systems with the same endianness.
Out of rage, I also added support for Dtype.itemsize property access.
Signed-off-by: Edward Z. Yang <ezyang@meta.com>
Pull Request resolved: https://github.com/pytorch/pytorch/pull/99834
Approved by: https://github.com/voznesenskym
