Fix currentWorkingDirectory

[kojirou1994]

String.init(cString:) may change the content

[jakepetroules]

Actually, this will break Windows because the platform string types won't match (UTF-16 != UTF-8). And Windows needs to use GetCurrentDirectoryW in order to support Unicode paths.

As an aside, according to POSIX, passing nil to getcwd is undefined behavior.

Essentially, we need to copy this: https://github.com/swiftlang/swift-foundation/blob/7002497ffceeeaf4916e06fd206724f1f801d2b5/Sources/FoundationEssentials/FileManager/FileManager%2BDirectories.swift#L494

[jakepetroules]

@iCharlesHu Is there any reason not to use FileManager.default.currentDirectoryPath for this?

[iCharlesHu]

@iCharlesHu Is there any reason not to use FileManager.default.currentDirectoryPath for this?

This package can't hard depend on Foundation because it's optional via a trait.