dbr quant: make QTensorInfo a dataclass and add orig_dtype (#71245)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/71245
This is a refactor to make a future PR of making observer
insertion be a separate pass easier.
1. adds orig_dtype, so we always record what was seen while tracing
2. switches from namedtuple to dataclass, so we can have more explicit types
Test Plan: CI and mypy
Reviewed By: HDCharles
Differential Revision: D33558281
Pulled By: vkuzo
fbshipit-source-id: b9f87e25a3538fee145f020916a31699046a9c11
(cherry picked from commit 3c8db243605220e990e3c7280ed475d6e90c32fb)
