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

[Sam Clegg via llvm-commits]

sbc100 wrote:

> True. I'm not sure I want to reorganize the whole thing but we could rename the directory from Wasm (which the object format is usually called) to WebAssembly (the architecture)😄

I think maybe go for a full rename for ELF and COFF too?  See what the other maintainers think about it?

Also, we have not yet used "Wasm" as a file or directory name in llvm.   We have `WebAssembly` and `wasm` and `WASM` in different places.   I'd like to fix that last one especially but I'm worried about such renames for case insensitive filesystem folks.

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