[cxx-interop] Class declaration order does not matter

Looking through the old issues found one that we already fixed. Adding a
a test to close the issue. Closing swiftlang#70336.

rdar://119405019

Author: Gabor Horvath

test/Interop/SwiftToCxx/class/swift-class-ordering.swift

@@ -9,3 +9,13 @@ public class SwiftNode {
 public struct SwiftLinkedList {
   public var head: SwiftNode
 }
+
+public class B
+{
+    public init() {}
+}
+
+public class A
+{
+    public init(_ b: B) {}
+}