[quant] Refactor test files (#36964)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/36964
Rename and restructure quantization related tests
https://github.com/pytorch/pytorch/issues/31625
Test Plan:
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Imported from OSS
Differential Revision: D21192509
fbshipit-source-id: 148c93e86e0ea68ab18a067fe74a8035a29a1e4e
