[llvm] [WebAssembly] getMemoryOpCost and getCastInstrCost (PR #122896)

[Thomas Lively via llvm-commits]

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

Mostly rubber-stamp LGTM since I'm not familiar with this area of the code, but it looks reasonable.

https://github.com/llvm/llvm-project/pull/122896