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/TuplesTest/pairEquals.kt

@@ -0,0 +1,14 @@
+import kotlin.test.*
+import kotlin.test.assertTrue
+import kotlin.test.assertEquals
+import kotlin.test.assertNotEquals
+
+val p = Pair(1, "a")
+val t = Triple(1, "a", 0.07)
+fun box() {
+    assertEquals(Pair(1, "a"), p)
+    assertNotEquals(Pair(2, "a"), p)
+    assertNotEquals(Pair(1, "b"), p)
+    assertTrue(!p.equals(null))
+    assertNotEquals("", (p as Any))
+}