String interpolation, after a healthy debate on discord

[ManKey]

On Thursday, 9 December 2021 at 21:06:11 UTC, WebFreak001 wrote:
> We had an argument on the discord about the

IMHO, this can be done through string mixins. But mixins have a 
large syntax (This is very strange for a language in which 
closures can be written as `{code}`.). If it was possible to 
write instead of `mixin(i!"2 + 3 = ${2 + 3}")` something like 
this `#i!"2 + 3 = ${2 + 3}"`, then this DIP would not be needed. 
Then it would be possible not only to do string interpolation, 
for example:
```d
JSON j = #jsonlit!q{
	"any" ~ "d_expr": 5 + 6,
	"key": data.map!(func).array,
};
```