[llvm] [Object][Wasm] Move wasm Object tests into their own directory (NFC) (PR #81072)

[Fangrui Song via llvm-commits]

MaskRay wrote:

Creating `test/Object/wasm` looks good to me. I'd prefer `wasm/` instead of `Wasm/` since `wasm/` is used more common.

We've moved ELF/COFF/Mach-O tests for at least llvm-readobj/llvm-objcopy/llvm-objdump.

https://github.com/llvm/llvm-project/pull/81072