Fix RPC Python User Function Error Handling (#63406)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/63406
The `RemoteException` will be thrown on the caller side when converting
the response message to IValue. Since it is a Python error, the error
message needs to be extracted explicitly and clear the `PyErr`.
Test Plan: Imported from OSS
Reviewed By: rohan-varma, ngimel
Differential Revision: D30372741
Pulled By: mrshenli
fbshipit-source-id: 1f72a7ee0c39cc2ef070f99884c142f7b3e0543d
