WASI-common wrappers for Lucet

A crate to use the reference WASI implementation in WebAssembly modules run with Lucet.

• Call wasi_common_lucet::export_wasi_funcs() once in order to have the symbols exported
• Create a new isntance with WasiCtx::new(). Note that the function signature slightly differs from the lucet-wasi one.
• Register it into Lucet instances using insert_embed_ctx().

```rust use wasicommonlucet::WasiCtx;

fn doit() -> Result <(), Error> { wasicommonlucet::exportwasifuncs(); // ... let mut lucetinstancehandle = lucetdylib.instantiate(region)?; let wasictx: WasiCtx = WasiCtx::new(["app"].iter())?; lucetinstancehandle.insertembedctx(wasi_ctx); // ... } ```