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/MapTest/plusAny.kt

@@ -0,0 +1,17 @@
+import kotlin.test.*
+
+fun <K, V> testPlusAny(mapObject: Any, pair: Pair<K, V>) {
+    val map = mapObject as Map<*, *>
+    fun assertContains(map: Map<*, *>) = assertEquals(pair.second, map[pair.first])
+
+    assertContains(map + pair)
+    assertContains(map + listOf(pair))
+    assertContains(map + arrayOf(pair))
+    assertContains(map + sequenceOf(pair))
+    assertContains(map + mapOf(pair))
+}
+
+fun box() {
+    testPlusAny(emptyMap<String, String>(), 1 to "A")
+    testPlusAny(mapOf("A" to null), "A" as CharSequence to 2)
+}