Update base for Update on "[ET-VK] De vectorise conv2d pw shader to improve perf."

This diff optimizes the performance of the `conv2d_pw` shader by de-vectorizing its implementation.

*   The original vectorized implementation of the `conv2d_pw` shader has been replaced with a de-vectorized approach to improve performance.
*   The `sum` array has been redefined to hold `float` values instead of `vec4` to accommodate the de-vectorized computation.

These changes seem to allow shader compiler to better optimize operations within the shader hence improving perf.

Differential Revision: [D75307267](https://our.internmc.facebook.com/intern/diff/D75307267/)

[ghstack-poisoned]

Author: trivedivivek