static map as a type function

[Per Nordlöw]

On Wednesday, 23 September 2020 at 10:51:41 UTC, Stefan Koch 
wrote:
> On Wednesday, 23 September 2020 at 09:46:54 UTC, Stefan Koch 
> wrote:
>
>> That should be surprising since type functions are just 
>> regular functions that happen to accept types as arguments ;)
>
> I meant that should _not_ be surprising.

Great work. Has Andrei given any advice on how to proceed 
regarding dip, reviews and acceptance? I presume this will get 
merged behind a -preview if it gets merged.