spirv-fuzz: Determine if two pointers point to different memory regions

[Vasniktel]

Currently, there is no way to tell if two pointers point to the different memory locations. That being said, DataSynonym fact is not enough.

We could implement some interesting transformations if we had a way to determine this. In particular, we could improve support for memory instructions in TransformationMoveInstructionDown.

[Vasniktel]

I've thrown this here "just in case". Maybe it is better not to implement some general-purpose machinery and instead focus on a particular use case.