Use of structs in Roto

[tertsdiepraam]

Currently, structs are hacked in with workarounds instead of using the cranelift functionality. Unfortunately cranelift documentation on this is a bit sparse. So I'll be collecting useful links here to see if I can put all the necessary information together.

• https://bytecodealliance.zulipchat.com/#narrow/stream/217117-cranelift/topic/.E2.9C.94.20How.20to.20work.20with.20structs.3F
• https://bytecodealliance.zulipchat.com/#narrow/stream/217117-cranelift/topic/Question.20about.20passing.20structs.20by.20value
• https://docs.rs/cranelift-codegen/latest/cranelift_codegen/ir/enum.ArgumentPurpose.html
• https://github.com/capy-language/capy/tree/master/crates/codegen/src/convert/abi