Julia IR level verification

Instead of only detecting things at the LLVM level, we should consider also doing so at the Julia level where much more information is still available. https://github.com/JuliaLang/julia/pull/57530 could probably serve as inspiration.

That said, we probably don't want to completely get rid of the LLVM IR verifier, or we'd have to accurately model how codegen behaves.

Start by reading Julia PR #57530 and tracing the existing LLVM IR verifier in GPUCompiler.jl. Determine how Julia-level verification could complement, rather than replace, LLVM verification; done criteria should specify the checks and their interaction.

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