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

[Sam Clegg via llvm-commits]

sbc100 wrote:

This makes some logical sense but the other sub-directories here represent architectures, and not object formats.  For example note that there are no COFF or ELF sub-directories here.   Should we move those tests too?

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