[quant][core][gpu] Wrapped CacheKey in Conv.cpp with anonymous namespace (#74543)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/74543
This is done to prevent ODR issues with other cudnn ops and we want to make sure
that the CacheKey in Conv.cpp is only used within this file. Other cudnn ops will
also define CacheKey in their files.
This PR should introduce no functional changes.
Test Plan:
In pytorch main directory, execute
```
python test/test_quantization.py TestQuantizedConv.test_qconv2d_cudnn
```
for accuracy testing and
```
python test/test_quantization.py TestQuantizedConv.test_benchmark
```
for benchmark testing.
Reviewed By: jerryzh168
Differential Revision: D35066248
Pulled By: dzdang
fbshipit-source-id: 35ee55a4a140a96cba969ebf1b572c35b4822af8
(cherry picked from commit f8637b2319c9bfb067363549f5aee0d6d1e8422d)
