[proposal] Dead Store Elimination Pass

[MaxGraey]

It will be great to have DSE pass. We have real world example where it can by useful:
AssemblyScript/assemblyscript#1785 (comment)

[MaxGraey]

Pretty interesting article. It seems DSE might be useful even after LLVM's pipeline:
https://blog.trailofbits.com/2018/07/06/optimizing-lifted-bitcode-with-dead-store-elimination

And I think it could be definitely useful for wasm GC