get rid of dynamic_cast in Quantizer (#25001)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/25001
Seems QScheme and Quantizer class type has 1-1 mapping, so use it to compare whether
two quantizers are equal instead of using dynamic_cast.
This way the code can remain mobile friendly as our internal mobile build doesn't
enable rtti by default.
ghstack-source-id: 88925243
Test Plan:
- builds;
- will check CI tests;
Differential Revision: D16951501
fbshipit-source-id: 585b354f64e5188fd34f01d456c91cec232ba6b0
