[ONNX] Use human readable enum for dtype scalars (#66822) (#67807)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/67807
Also make quoting of string literals consistent.
Test Plan: Imported from OSS
Reviewed By: msaroufim
Differential Revision: D32181309
Pulled By: malfet
fbshipit-source-id: e1053701e3589f0310d8b5ef920359c03c6713f0
