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().

use wasi_common_lucet::WasiCtx;

fn doit() -> Result <(), Error> {
    wasi_common_lucet::export_wasi_funcs();
    // ...
    let mut lucet_instance_handle = lucet_dylib.instantiate(region)?;
    let wasi_ctx: WasiCtx = WasiCtx::new(["app"].iter())?;
    lucet_instance_handle.insert_embed_ctx(wasi_ctx);
    // ...
}