[turbopack] Remove WebAssembly helpers from the default runtime (#94373)
This PR builds on https://github.com/vercel/next.js/pull/94372. It does
a similar thing but for the WebAssembly-related helpers. Collectively,
these cut the run time by about 2KB (5%).
The WebAssembly-related module is inserted within
`turbopack-wasm/src/loader.rs`. Similar design questions to #94372
exist. `RUNTIME_ROOT` is added to `contextPrototype` and the JS-code
lives in the `turbopack-wasm` package.