Ability to create pointers to Workgroup/Shared memory in shaders

Feature request for workgroup/shared memory pointers.

Ideally we could get pointers to workgroup/shared memory like in cuda/opencl.

```
void foo(float * ptr){
...
}

...

shared float x[32];
foo(&x);

```

On the vulkan discord there was discussion after the first vulkanized event about the fact in hardware, there are performance considerations for being able to deal with *both* shared/global pointers in a function. So for the purposes of this feature request, the only thing actually being requested is the features of PhysicalStorageBuffer, but for *just* the workgroup storage class.

This would allow us to

* re-interpret cast data
* more easily target SPIR-V as a language
* more easily write functions in GLSL (as BufferDeviceAddress/and physicalstoragebuffer allowed us to do)

Start with issue 1756 and review the requested workgroup/shared memory pointer behavior alongside the mentioned PhysicalStorageBuffer, SPIR-V, GLSL, CUDA, and OpenCL concepts. Determine the required Vulkan specification changes and how support should be described; done means the feature is specified consistently with the requested workgroup-only scope.

Written by the indexing model from the issue text.