[vulkan] fixed calling of threshold op (#79717)
Summary: implemented threshold op for vulkan (realized it was not being called and the shader was in the wrong folder so had to fix that)
Test Plan: buck run //xplat/caffe2:pt_vulkan_api_test_binAppleMac
Differential Revision: D37210717
Pull Request resolved: https://github.com/pytorch/pytorch/pull/79717
Approved by: https://github.com/SS-JIA
