Add type-hint check for default arguments in TorchScript C++ frontend (#39021)
Summary:
This PR fixes https://github.com/pytorch/pytorch/issues/39020 by requiring users to type-hint default arguments to a TorchScript when using the C++ frontend (the Python frontend will insert those automatically).
Since this is a bit of a niche use case, I opted for the simpler solution of making type-hints mandatory for default arguments, as opposed to trying to type-infer them. I left a comment in the code justifying this choice.
Test is included.
/cc t-vi
Pull Request resolved: https://github.com/pytorch/pytorch/pull/39021
Differential Revision: D21755317
Pulled By: suo
fbshipit-source-id: e007650d3bfb3a4c58c25ad2c3a17759898f303b
