Update on "[ET-VK][Ops] aten.avg_pool2d"

## The Operator
`nn.Module` invocations of [`torch.nn.AvgPool2d`](https://pytorch.org/docs/stable/generated/torch.nn.AvgPool2d.html) get compiled to `aten.avg_pool2d.default` in the Edge Dialect, which carries the following signature.
```
- func: avg_pool2d(Tensor self, int[2] kernel_size, int[2] stride=[], int[2] padding=0, bool ceil_mode=False, bool count_include_pad=True, int? divisor_override=None) -> Tensor
```

## Implementation
This is a full implementation. We start with [LiteInterpreter's `avg_pool2d.glsl` logic](https://github.com/pytorch/pytorch/blob/9257a0698b57acc5607ee6fe31a16fdd93af1731/aten/src/ATen/native/vulkan/glsl/avg_pool2d.glsl), which is incomplete, and cover `ceil_mode=True`,  `count_include_pad=True`, and `divisor_override` cases for full support. As a result, the divisor's computation is now a bit complex. If needed, we can simplify it into separate shaders in the future.

Differential Revision: [D57918523](https://our.internmc.facebook.com/intern/diff/D57918523/)

[ghstack-poisoned]

Author: jorgep31415

backends/vulkan/runtime/graph/ops/impl/Pool.cpp

@@ -124,13 +124,12 @@ void max_pool2d(ComputeGraph& graph, const std::vector<ValueRef>& args) {
 //
 
 struct DivisorParams final {
-  int32_t divisor;
+  int32_t divisor_override;
   bool count_include_pad;
 };
 
 DivisorParams create_divisor_params(
     ComputeGraph& graph,
-    const api::utils::ivec2& kernel_size,
     const ValueRef divisor_override,
     const ValueRef count_include_pad) {
   return {
@@ -165,8 +164,8 @@ void add_avg_pool2d_node(
   Kernel2dParams kernel_params =
       create_kernel2d_params(graph, kernel_size, stride, padding);
 
-  DivisorParams divisor_params = create_divisor_params(
-      graph, kernel_params.kernel_size, divisor_override, count_include_pad);
+  DivisorParams divisor_params =
+      create_divisor_params(graph, divisor_override, count_include_pad);
 
   graph.execute_nodes().emplace_back(new ExecuteNode(
       graph,