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/OrderingTest/combineComparators.kt

@@ -0,0 +1,26 @@
+import kotlin.test.*
+
+import kotlin.comparisons.*
+
+data class Item(val name: String, val rating: Int) : Comparable<Item> {
+    public override fun compareTo(other: Item): Int {
+        return compareValuesBy(this, other, { it.rating }, { it.name })
+    }
+}
+
+val v1 = Item("wine", 9)
+val v2 = Item("beer", 10)
+val v3 = Item("apple", 20)
+fun box() {
+    val byName = compareBy<Item> { it.name }
+    val byRating = compareBy<Item> { it.rating }
+    val v3 = Item(v1.name, v1.rating + 1)
+    val v4 = Item(v2.name + "_", v2.rating)
+    assertTrue((byName then byRating).compare(v1, v2) > 0)
+    assertTrue((byName then byRating).compare(v1, v3) < 0)
+    assertTrue((byName thenDescending byRating).compare(v1, v3) > 0)
+
+    assertTrue((byRating then byName).compare(v1, v2) < 0)
+    assertTrue((byRating then byName).compare(v4, v2) > 0)
+    assertTrue((byRating thenDescending byName).compare(v4, v2) < 0)
+}