Align with the new Wasm testsuite

The Webassembly/testsuite changed a bit structure, and moved the tests around, we should reflect the changes to get a green CI again.

Getting everything to pass requires a bit more work than expected, pinning the testsuite and asking for guidance meanwhile:
https://github.com/WebAssembly/testsuite/pull/129#issuecomment-3108787966