This makes two changes to prepare for incoming changes to skwasm in the web engine:
* We will (at least for now) be depending on the `WebAssembly.Function` constructor in `skwasm`, which is hidden behind the `--experimental-wasm-type-reflection` flag. We need to pass that when running skwasm benchmarks.
* We are going to be upgrading the skwasm build to a newer version of emscripten, which exposes the wasm exports via the `wasmExports` property instead of the `asm` property. Make sure to support either, if passed.