Add FoldToASCII functions for strings

[Idhrendur]

See ParadoxGameConverters/PGCG.commonItems#197 (comment) for the inspiration

[Idhrendur]

We already have string conversion functions.

[Zemurin]

This is for normalization of non-ascii into ascii strings manually because convert[xxyy]toASCII inserts 0 for chars it can't convert.

[IhateTrains]

You could use the C implementation of AnyAscii for this:
https://github.com/anyascii/anyascii#anyascii

I've just switched to using the C# version of this in commonItems.NET.