draft proposal for Sum Types for D

[Per Nordlöw]

On Tuesday, 29 November 2022 at 06:26:20 UTC, Walter Bright wrote:
> Go ahead, Make My Day! Destroy!
>
> https://github.com/WalterBright/DIPs/blob/sumtypes/DIPs/1NNN-(wgb).md

Regarding

```d
sumtype Result
{
     Error,
     int Value
}
```

, is

```d
Result res;
res = 25;
```

supposed to be supported aswell? If so, why not --- because it 
requires implicit conversion?