message: Generate UnpackValue in starlark_simple_value macro
diff: @@ -165,6 +165,12 @@ macro_rules! starlark_simple_value {
  }
  }
  + impl<'v> $crate::values::UnpackValue<'v> for &'v $x {
  + fn unpack_value(x: $crate::values::Value<'v>) -> Option<&'v $x> {
  + $x::from_value(x)
  + }
  + }
  +
  impl<'v> $crate::values::FromValue<'v> for $x {
  fn from_value(x: $crate::values::Value<'v>) -> Option<$crate::values::ARef<'v, Self>> {
  $x::from_value(x).map(|x| $crate::values::ARef::new_ptr(x))
  