Update on "[ET-VK][7/n] Slice, with lots of codegen improvements"

1. Add slice operation. Instead of using copy in LI, we implement a simple shader with offsets.

2. Improvement in codegen.
- add support of optional variables
- improve indent of the code, for better readability
- allow user to specify tensor value generation, possible to generate sequential values for easier debugging for index operations
- sample code improve test-case specification, particularly with long and optional values.

Differential Revision: [D56295985](https://our.internmc.facebook.com/intern/diff/D56295985/)

[ghstack-poisoned]

Author: yipjustin

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

@@ -8,16 +8,13 @@
 
 #include <executorch/backends/vulkan/runtime/graph/ops/OperatorRegistry.h>
 
-#include <executorch/backends/vulkan/runtime/api/api.h>
 #include <executorch/backends/vulkan/runtime/graph/Logging.h>
 
 #include <executorch/backends/vulkan/runtime/graph/ops/impl/utils/DimUtils.h>
 #include <executorch/backends/vulkan/runtime/graph/ops/impl/utils/KernelUtils.h>
 #include <executorch/backends/vulkan/runtime/graph/ops/impl/utils/TensorUtils.h>
 #include <executorch/backends/vulkan/runtime/graph/ops/utils/ShaderNameUtils.h>
 
-#include <iostream>
-
 namespace vkcompute {
 
 void add_slice_tensor_out_node(