Apple rewriting Foundation in Swift

In December 2022, Apple announced it was writing a new Foundation 
implementation without any CoreFoundation dependencies called 
swift-foundation [1][2].

They have begun to replace many classes in Darwin's Foundation.framework 
with swift-foundation, starting with Darwin 23 (macOS 14 Sonoma; iOS 17; 
Xcode 15; Swift 6). This included JSONDecoder, URL, Calendar, 
FileManager, ProcessInfo, along with the newly introduced classes and 
APIs such as FormatStyle, ParseStrategy, Predicate, and JSON5, 
Expression, calendar enumeration improvements, calendar recurrence 
rules, format style enhancements.

Back in 2024, I intended to write a more detailed message to this list 
about the issue, but that clearly didn't happen. It would be extremely 
helpful if somebody could look at the sources I found back then, and 
maybe some more recent discussions on the Swift forums, and update 
everyone here about these developments; I think they are very relevant 
to the project. If nobody can do that, I might be able to do so in a few 
weeks, but I'm still quite busy.

[1] https://www.swift.org/blog/future-of-foundation/
[2] https://forums.swift.org/t/what-s-next-for-foundation/61939


* https://forums.swift.org/t/any-updates-on-the-new-foundation/68532
* https://www.swift.org/blog/foundation-preview-now-available/
*
* https://github.com/swiftlang/swift-corelibs-foundation/issues/5001
* https://forums.swift.org/t/swift-foundation-now-available/73530a
* https://github.com/swiftlang/swift-foundation
* https://github.com/swiftlang/swift-corelibs-foundation/issues/5001