[ET-VK] Fixing conv2d dw incorrect output when stride != dilation issue. (#7628)

Pull Request resolved: https://github.com/pytorch/executorch/pull/7595

This diff moves current implementation of conv2d dw as a special case when stride equals dilation in the Vulkan backend of Executorch, since that's the only time this kind of caching is possible.

If stride does not equal dilation the old implementation is used.

Additional test cases are added to ensure computation is correct when stride != dilation.
ghstack-source-id: 261183385
@exported-using-ghexport

Differential Revision: [D67908916](https://our.internmc.facebook.com/intern/diff/D67908916/)

Co-authored-by: Vivek Trivedi <5340687+trivedivivek@users.noreply.github.com>