Move HashSet-wasm to first, worst, average scoring

Same steps as for the other Wasm line items:
- Move files to subdirectory.
- Rebuild with up-to-date Emscripten.
- Reduce single iteration time, so that we can run multiple iterations (a single iteration before took ~300ms, now ~30ms).
- Checked that we spend roughly the same amount of CPU samples in the top-tier and that overall profiles look similar.