Remove SetCode() copy in shader instrumentation

We have this code

```c++
// TODO - This makes a copy, but could save on Chassis stack instead (then remove function from VUL).
// The core issue is we always use std::vector but Safe Struct manages its own version of the pCode
// memory. It would be much harder to change everything from std::vector and instead to adjust Safe Struct to not
// double-free the memory on us. If making any changes, we have to consider a case where the user inlines the
// fragment shader, but use a normal VkShaderModule in the vertex shader.
modified_shader_module_ci->SetCode(instrumented_spirv);
```

What is needed is a way in VUL to allow the safe struct to let us manage the memory

Start by tracing the shader instrumentation code around modified_shader_module_ci->SetCode(instrumented_spirv), then inspect the VUL safe-struct ownership of pCode and the mixed inline-fragment and normal-vertex shader case described in the issue. Done means VUL can let the safe struct use caller-managed memory without the SetCode copy or a double-free.

Written by the indexing model from the issue text.