Update base for Update on "[ET-VK] Using vec2 to store output positions to reudce shader register footprint."

The diff changes the use of `u16vec3` to `u16vec2` to store output positions in the conv2d_pw op. This change is made to reduce the shader register footprint and improve performance.

Differential Revision: [D67726229](https://our.internmc.facebook.com/intern/diff/D67726229/)

[ghstack-poisoned]

Author: trivedivivek