Macro golang_type_decl::gen_type_alias

macro_rules! gen_type_alias {
    ($code:literal) => { ... };
    (
        $code:literal,
        $type_:ty
    ) => { ... };
    (
        $code:literal,
        $( $opt_k:ident = $opt_v:literal ),+ $(,)?
    ) => { ... };
    (
        $code:literal,
        $type_:ty,
        $( $opt_k:ident = $opt_v:literal ),+ $(,)?
    ) => { ... };
}