Replace partial MiniFoundation with FoundationEssentials

[keeshux]

Give up on the overwhelming –and dumb– task of replacing Foundation completely. The footprint with FoundationEssentials is only marginally bigger, for dramatic benefits. If going serious at some point, dropping Swift would be a much wiser choice in the future.

Basically, merge MiniFoundation Native and Compat targets. Then export Foundation on Apple, and FoundationEssentials everywhere else. In the latter case, add some custom code behind the MINIF_COMPAT symbol to attain feature-parity with Foundation for the sake of the library.

MiniFoundation folders:

• Foundation (Apple)
• FoundationCompat (cross)
• FoundationEssentials (Apple and cross)
• Everything else is shared as before

Steps:

• Delete SWON, rely on Codable/JSONEncoder/JSONDecoder
• Delete redundant reimplementations (Data, Date, FileManager, URL, UUID)
• Delete unused C code
• Delete "mini" wrappers in the middle (e.g. MiniURLProtocol)
• Return contents of URL path, not of a generic URL (would potentially require networking)
• Implement compatible regular expressions in C++ (still targeting Swift 5.x)
• Always export Dispatch
• Disambiguate UUID on Windows

CMake issues:

• Enforce FoundationEssentials autolinked libs manually in Linux/Android toolchains (dynamic linking failure if autolinked libs are not provided)

[keeshux]

Doubts:

1. Given a file URL, this method is not available in FoundationEssentials and therefore reimplemented this way.

Are these methods equivalent?

• FileManager.contentsOfDirectory(atPath: url.path)
• FileManager.contentsOfDirectory(at: url)

public func contentsOfDirectory(at url: URL) throws -> [URL] {
    let items = try contentsOfDirectory(atPath: url.filePath())
    return items.map {
        URL(filePath: $0, relativeTo: url)
    }
}

2. Are we overriding too much in the FoundationEssentials folder, given that Apple Foundation doesn't need manual implementations?

Specifically:

• FileManager.contentsOfDirectory(at:)
• String.replacingOccurrences(of:with:)