[llvm] [SPIR-V] Re-implement switch and improve validation of forward calls (PR #87823)

[Michal Paszkowski via llvm-commits]

https://github.com/michalpaszkowski approved this pull request.

LGTM! Apologies for this taking so long... needed to dig out older versions of benchmarks. I remember switches used to be quite sensitive point for performance. No significant differences here.

https://github.com/llvm/llvm-project/pull/87823