Derive Macro starlark::values::StarlarkAttrs

#[derive(StarlarkAttrs)]
{
    // Attributes available to this derive:
    #[starlark]
}

Derive accessor methods that are designed to be used from {has,get,dir}_attr in an impl StarlarkValue block. All fields in the struct that are not marked with #[starlark(skip)] are exported to Starlark code as attributes. NOTE: Any usage must also call starlark_attrs!() in the impl block for StarlarkValue, otherwise the generated attr methods will not be used.