message: feat(depreacted) Port `Func.signature` from `DynFunc`.
  So that `Func` can be used in place of `DynFunc`.
diff: @@ -74,12 +74,16 @@ impl Func {
  }
  }
  + pub fn signature(&self) -> &FuncDescriptor {
  + &self.signature
  + }
  +
  pub fn params(&self) -> &[Type] {
  - self.signature.params()
  + self.signature().params()
  }
  pub fn returns(&self) -> &[Type] {
  - self.signature.results()
  + self.signature().results()
  }
  pub fn call(&self, params: &[Value]) -> Result<Box<[Value]>, RuntimeError> {
  