Fix Hash(c10::Scalar), account for garbage data in union (#68201)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/68201
Hash(c10::Scalar) made a bad assumption that it was valid to just hash over all the bytes of data of the c10::Scalar struct.
Becuase c10::Scalar stores a union of different (float/int/complex) types with different sizes, not all bytes are valid in all cases. Hash() should only read the bytes corresponding to the currently active type.
Test Plan: Added new unit tests. Verified HashTest.Scalar failed with the original Hash() impl and then fixed.
Reviewed By: alanwaketan
Differential Revision: D32367564
fbshipit-source-id: ac30dd4f6dd0513954986d3d23c0c11ba802c37b
