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/text/StringNumberConversionTest/intToStringWithRadix.kt

@@ -0,0 +1,11 @@
+import kotlin.test.*
+
+
+fun box() {
+    assertEquals("-ff", (-255).toString(radix = 16))
+    assertEquals("1100110", 102.toString(radix = 2))
+    assertEquals("kona", 411787.toString(radix = 27))
+    assertFailsWith<IllegalArgumentException>("Expected to fail with radix 37") { 37.toString(radix = 37) }
+    assertFailsWith<IllegalArgumentException>("Expected to fail with radix 1") { 1.toString(radix = 1) }
+
+}