[vulkan] Add mean.dim op for vulkan (#47312)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/47312
Test Plan:
```
cd ~/pytorch
BUILD_CUSTOM_PROTOBUF=OFF \
BUILD_TEST=ON \
USE_EIGEN_FOR_BLAS=OFF \
USE_FBGEMM=OFF \
USE_MKLDNN=OFF \
USE_NNPACK=OFF \
USE_NUMPY=OFF \
USE_OBSERVERS=OFF \
USE_PYTORCH_QNNPACK=OFF \
USE_QNNPACK=OFF \
USE_VULKAN=ON \
USE_VULKAN_API=ON \
USE_VULKAN_SHADERC_RUNTIME=ON \
USE_VULKAN_WRAPPER=OFF \
MACOSX_DEPLOYMENT_TARGET=10.9 CC=clang CXX=clang++ python3 setup.py develop --cmake && ./build/bin/vulkan_api_test
```
Reviewed By: IvanKobzarev
Differential Revision: D24713617
Pulled By: SS-JIA
fbshipit-source-id: 20c0f411fb390ad2114c7deff27cc6fc77448089
