Add Package::from_wit convenience #92

let mut resolve = wit_parser::Resolve::new();
let pkg = if path.is_dir()
   let (pkg, _) = resolve.push_dir(path)?;
   pkg
} else {
  let unresolved = wit_parser::UnresolvedPackage::parse_file(&path)?;
  resolve.push(unresolved)?
};
let bytes = wit_component::encode(Some(true), &resolve, pkg)?;
wac_graph::types::Package::from_bytes(
  name,
  None,
  bytes.to_owned(),
  types,
)