[pytorch] recast infer_type error and amend with name and item that failed inferring
Summary:
When type inference fails when JITing torchscript module, the error message does not give any implication where the error fails. For example: "Cannot create dict for key type 'int?', only int, float, complex, Tensor and string keys are supported".
This adds the variable name and item to the error message.
Reviewed By: ajaech
Differential Revision: D26327483
fbshipit-source-id: d8c85e7550258d7c56530f5826ff9683ca8b2b94
