The files in Tools/wasm are a little messy as nearly all Emscripten-related files are in emscripten/ while the WASI-related files are not. So I want to:

• Add a wasi/ directory and move code related to wasi.py there
• Make wasi.py a deprecated shim for calling wasi/
• Update CODEOWNERS such that @freakboy3742 isn't bothered about WASI-only stuff and I'm not bothered about Emscripten-only stuff

Linked PRs

• [3.14] GH-133600: Backport file reorg of Tools/wasm/wasi #135950
• gh-133600: Move config.site-wasm32-emscripten into the emscripten folder #136934
• [3.14] gh-133600: Move config.site-wasm32-emscripten into the emscripten folder (GH-136934) #136956
• gh-133600: Run Tools/wasm/wasi on CI instead of deprecated Tools/wasm/wasi.py #140907
• [3.14] gh-133600: Run Tools/wasm/wasi on CI instead of deprecated Tools/wasm/wasi.py (GH-140907) #140964