[vulkan] Rewrite prepacking functions using aten functions + some code cleanup (#84973)
Rewrites the convolution prepacking function using aten ops, removing a large amount of redundant code. Adds detailed comments describing the transformations that are performed. Also cleans up some unneeded code.
Differential Revision: [D39486489](https://our.internmc.facebook.com/intern/diff/D39486489/)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/84973
Approved by: https://github.com/salilsdesai
