[llvm] [VectorCombine] Prevent extract/ins rewrite to GEP (PR #150216)

[Nathan Gauër via llvm-commits]

Keenuts wrote:

> For the same reason, we use `@llvm.preserve.*.access.index` instead of gep to preserve type information on BPF. Is it also suitable for SPIR-V?

This is one of the solutions I'm exploring to fix the issue long-term, and for now our best one. But I need to evaluate the impact on optimizations (as we require some for legalization). So getting structured gep in a robust way will take time (hence why this PR)

https://github.com/llvm/llvm-project/pull/150216