Update on "[EK-VT] Replacing the use of uvec3 with WorkgroupSize class to reduce memory usage and improve processing speed"

This diff replaces the use of `uvec3` with `WorkgroupSize` class to reduce memory usage and improve processing speed in the Vulkan backend of Executorch.

Differential Revision: [D70021032](https://our.internmc.facebook.com/intern/diff/D70021032/)

[ghstack-poisoned]

Author: trivedivivek

backends/vulkan/runtime/utils/VecUtils.h

@@ -499,7 +499,7 @@ class WorkgroupSize final {
     // shift numbers by multiple of 11 bits, since each local workgroup axis can
     // be 1024 at most and which is 0x400. only z axis can't store 1024, because
     // it would overflow uint32_t storage.
-    if (z == 1024) {
+    if (vec[2u] == 1024) {
       throw std::runtime_error(
           "Workgroup size in z axis cannot be 1024 because it would overflow uint32_t storage");
     }