Write new errorString() swift macro

[tmolitor-stud-tu]

Write a ObjcC macro and a Swift macro doing extracting the localized error message from an NSError object and taking an optional fallback string that automatically gets wrapped in NSLocalizedString().

The ObjC macro would be this:

#include "metamacros.h"
#define errorString(error, ...) metamacro_if_eq(0, metamacro_argcount(__VA_ARGS__))( emptyDefault(((NSError*)error).userInfo[NSLocalizedDescriptionKey], @"", NSLocalizedString(@"Unknown error!", @"")) )( emptyDefault(((NSError*)error).userInfo[NSLocalizedDescriptionKey], @"", NSLocalizedString(metamacro_head(__VA_ARGS__), @"")) )

Swift macro resources, that should be helpful:
https://www.avanderlee.com/swift/macros/

https://docs.swift.org/swift-book/documentation/the-swift-programming-language/macros/

https://github.com/krzysztofzablocki/Swift-Macros?tab=readme-ov-file

This can be a follow up PR, but don't forget that (we'll need that NSError to string conversion a lot when we use promises)

See #1338 (comment)