Move overloaded_args from FunctionSignature to PythonArgs (#106983)
This moves the `overloaded_args` field from FunctionSignature to PythonArgs. FunctionSignature is shared by all calls and should be immutable. PythonArgs contains the parsing results for an single call to the PyTorch API.
I did not measure a difference in performance in the "overrides_benchmark", although I expect there to be a bit more work in the common case. Note that the noise factor for the benchmark is much larger than the differences reported below:
Before:
```
Type tensor had a minimum time of 2.3615360260009766 us and a standard deviation of 0.7833134150132537 us.
Type SubTensor had a minimum time of 10.473251342773438 us and a standard deviation of 0.1973132457351312 us.
Type WithTorchFunction had a minimum time of 5.484819412231445 us and a standard deviation of 0.13305981701705605 us.
Type SubWithTorchFunction had a minimum time of 11.098146438598633 us and a standard deviation of 0.15598918253090233 us.
```
After:
```
Type tensor had a minimum time of 2.2134780883789062 us and a standard deviation of 0.802064489107579 us.
Type SubTensor had a minimum time of 10.625839233398438 us and a standard deviation of 0.15155907021835446 us.
Type WithTorchFunction had a minimum time of 5.520820617675781 us and a standard deviation of 0.23115111980587244 us.
Type SubWithTorchFunction had a minimum time of 11.227846145629883 us and a standard deviation of 0.23032321769278497 us.
```
Fixes #106974
Pull Request resolved: https://github.com/pytorch/pytorch/pull/106983
Approved by: https://github.com/zou3519, https://github.com/ezyang, https://github.com/albanD
