Builtin for formatted strings

[dali99]

Is your feature request related to a problem? Please describe.
When implementing NixOS/nixpkgs#177273 a lookup table for ascii values had to be added.
This isn't very generic.

Describe the solution you'd like
A more general solution where we would have access to something more akin to printf via a builtin would simplify the code a lot.
And it would probably be useful for many other applications