Function write_submilli_array_struct 

pub fn write_submilli_array_struct(
    caller: &mut Caller<'_, StoreData>,
    elements: &[Val],
) -> Result<Rooted<StructRef>>

Build a real $Array (vtable + $rawArray backing) from already-built element object refs (e.g. $strings for a string[]). Each element Val must be a (ref null $Object) — a subtype ref or Val::AnyRef(None).