Fix setArgumentNames and make Script/Python consistent (#62442)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/62442
For PythonMethodWrapper::setArgumentNames, make sure to use the correct method
specified by method_name_ rather than using the parent model_ obj which itself
_is_ callable, but that callable is not the right signature to extract.
For Python vs Script, unify the behavior to avoid the 'self' parameter, so we only
list the argument names to the unbound arguments which is what we need in practice.
Test Plan: update unit test and it passes
Reviewed By: alanwaketan
Differential Revision: D29965283
fbshipit-source-id: a4e6a1d0f393f2a41c3afac32285548832da3fb4
