Support Vec<TransparentEnum>

[chinedufn]

This commit adds support for bridging Vec<TransparentEnum>.

For example, the following is now possible:

#[swift_bridge::bridge]
mod ffi {
    enum SomeEnum {
        VariantA,
        VariantB,
    }

    extern "Rust" {
        fn some_function(arg: Vec<SomeEnum>) -> Vec<SomeEnum>;
    }
}