tests: Copy stdlib tests from Kotlin/JVM

This patch copies Kotlin/JVM stdlib tests (libraries/stdlib/test)
excepting ones with explicit java dependencies. It also transforms
the tests to use them as box-tests.

backend.native/tests/external/stdlib/collections/IteratorsTest/iterationOverIterator.kt

@@ -0,0 +1,11 @@
+import kotlin.test.*
+
+
+fun box() {
+    val c = listOf(0, 1, 2, 3, 4, 5)
+    var s = ""
+    for (i in c.iterator()) {
+        s = s + i.toString()
+    }
+    assertEquals("012345", s)
+}