OpPtrAccessChain

SPIRV-Cross currently can't translate OpPtrAccessChain (provided by PhysicalStorageBuffer cap, among others) to GLSL.

It is not possible to translate all uses of OpPtrAccessChain into OpAccessChain on an unbounded array: OpPtrAccessChain can be used to compute pointer to one past the end using the element operand, while OpAccessChain can not. Considering this, I think translating the B+E part of OpPtrAccessChain (when used on a PhysicalStorageBuffer pointer) to integer arithmetic, and the remaining part to ordinary OpAccessChain is the way go. This loses pointer provenance information but is correct and as a nice bonus should be simple: the case when OpPtrAccessChain is just used to perform pointer arithmetic, without creating a pointer into an element, doesn't need any special handling.

Start by tracing the existing handling of OpAccessChain and the GLSL translation path for PhysicalStorageBuffer pointers. Determine how OpPtrAccessChain's B+E pointer arithmetic and one-past-the-end behavior should be represented, then verify that all stated uses translate correctly.

Written by the indexing model from the issue text.