Support enums with named data

[NiwakaDev]

This PR addresses #160 and adds support for enums with named data.

Here's an example of using this.

#[swift_bridge::bridge]
mod ffi {
    enum EnumWithNamedData {
        Variant1 { hello: String, data_u8: u8 },
        Variant2 { data_i32: i32 },
        Variant3,
    }

    extern "Rust" {
        fn reflect_enum_with_named_data(arg: EnumWithNamedData) -> EnumWithNamedData;
    }
}

func testEnumWithNamedData() {
    let enumWithNamedData1 = EnumWithNamedData.Variant1(hello: create_string("hello"), data_u8: 123)
    switch reflect_enum_with_named_data(enumWithNamedData1) {
    case .Variant1(let hello, let dataU8):
        XCTAssertEqual(hello.toString(), "hello")
        XCTAssertEqual(dataU8, 123)
    default:
        XCTFail()
    }
}

[chinedufn]

Mind surrounding your Rust example in a bridge module?

#[swift_bridge::bridge]
mod ffi {
    // ... 
}

[chinedufn]

Great work. One minor piece of feedback but otherwise looks good to me.

Thanks!

[chinedufn]

I think it would be clearer to do all of the field setting here instead of doing half of it here an half of it at the call site.

Maybe something like:

/// Create a string for setting the value of a struct's field.
///
/// Example if named field -> "field_name: someValue".
/// Example if unnamed field -> "someValue".
fn struct_field_setter_string(&self, value: String) -> String {
    match &self.accessor {
        NormalizedStructFieldAccessor::Named(name) => {
            format!("{}: {}", name.to_string(), value)
        }
        NormalizedStructFieldAccessor::Unnamed(_idx) => {
            value
        }
    }
}

[chinedufn]

Great stuff. Thanks!