PathCchIsRoot Updated isRoot extension.

Now that swiftlang/swift-foundation#976 and swiftlang/swift-foundation#980 are fixed we can clean this code up a bit by removing the empty path check on Linux and by using the native `PathCchIsRoot` on Windows.

Author: macshome

Sources/SwiftFormat/Utilities/URL+isRoot.swift

@@ -12,21 +12,19 @@
 
 import Foundation
 
+#if os(Windows)
+import WinSDK
+#endif
+
 extension URL {
   @_spi(Testing) public var isRoot: Bool {
-    #if os(Windows)
-    // FIXME: We should call into Windows' native check to check if this path is a root once https://github.com/swiftlang/swift-foundation/issues/976 is fixed.
-    // https://github.com/swiftlang/swift-format/issues/844
-    var pathComponents = self.pathComponents
-    if pathComponents.first == "/" {
-      // Canonicalize `/C:/` to `C:/`.
-      pathComponents = Array(pathComponents.dropFirst())
-    }
-    return pathComponents.count <= 1
+      guard isFileURL else { return false }
+      #if os(macOS)
+      return self.path == NSOpenStepRootDirectory()
+    #elseif os(Windows)
+      return self.path.withCString(encodedAs: UTF16.self, PathCchIsRoot)
     #else
-    // On Linux, we may end up with an string for the path due to https://github.com/swiftlang/swift-foundation/issues/980
-    // TODO: Remove the check for "" once https://github.com/swiftlang/swift-foundation/issues/980 is fixed.
-    return self.path == "/" || self.path == ""
+    return self.path == "/"
     #endif
   }
 }