[ET-VK] Allow int4 linear to execute without 8bit buffer support (#10234)

## Context

Some Vulkan devices do not have support for 8-bit buffers, which is currently required to execute the int4 linear compute shader due to the prepacking shader requiring it.

This diff bypasses that restriction by introducing a variant of the prepacking shader that does not need 8-bit buffers.

## Changes

Introduce a variant of the int4 weight prepacking shader that interprets the tensor data as an array of `uint` instead of `uint8_t`. Each `uint` represents 4 `uint8_t` values.

Differential Revision: [D72750897](https://our.internmc.facebook.com/intern/diff/D72750897/)