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/CollectionTest/joinTo.kt

@@ -0,0 +1,9 @@
+import kotlin.test.*
+import kotlin.comparisons.*
+
+fun box() {
+    val data = listOf("foo", "bar")
+    val buffer = StringBuilder()
+    data.joinTo(buffer, "-", "{", "}")
+    assertEquals("{foo-bar}", buffer.toString())
+}