[llvm] [SPIR-V] Add store legalization for ptrcast (PR #135369)

[Steven Perron via llvm-commits]

https://github.com/s-perron commented:

Could we please use OpVectorShuffle. Also, I nocited that existing OpVectorShuffle tests look wrong. In `@fooBounds` You have:

```
; CHECK: %[[#val:]] = OpVectorShuffle %[[#v3]] %[[#load]] %[[#load]] 0 0 0
```

I believe this should be:

```
; CHECK: %[[#val:]] = OpVectorShuffle %[[#v3]] %[[#load]] %[[#load]] 0 1 2
```

You can the first three element of the first input vector to be the first three elements of the output vector.

https://github.com/llvm/llvm-project/pull/135369