Opt-in for including argument names in ABI

[jmh530]

On Thursday, 17 September 2020 at 14:12:13 UTC, Seb wrote:
> tl;dr: `pragma(mangle, withArgumentNames:true)` would be a way 
> to tell the compiler to include the argument names in the ABI, 
> s.t. overloads with different names can be resolved.
>
> [snip]

I don't have an opinion on the options, but I do like the general 
approach. Concern about depreciations was my only issue with the 
DIP.