third draft: add bitfields to D

[Nick Treleaven]

On Friday, 5 July 2024 at 10:19:56 UTC, Nick Treleaven wrote:
> On Thursday, 4 July 2024 at 18:34:00 UTC, Steven Schveighoffer 
> wrote:
>> int[16] arr;
>> arr[value()] == 5; // VRP makes this valid
>> ```
>
> Did you mean `= 5`? If so the assignment already compiles, so 
> VRP would make no difference for that code.

Well, it would allow skipping the bounds check.