Add custom `VkInt4WeightOnlyQuantizer` for vulkan (#6234)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/6234

## Context

This diff adds the `VkInt4WeightOnlyQuantizer` class which enables 4-bit quantization of linear layers via source transformation. This quantizer class is copied from `torchao.quantization.GPTQ.WeightOnlyInt4Linear` with some minor changes as annotated in the implementation.

Note that the pt2e quantization flow does not yet support groupwise quantization, so source transformation is the only way to perform groupwise quantization at the moment.
ghstack-source-id: 248349848
exported-using-ghexport

Reviewed By: jorgep31415

Differential Revision: D64406457

fbshipit-source-id: 7d638d58414f2eb048caba60ebb11b7783bb3b7a