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/shortToStringWithRadix.kt

@@ -0,0 +1,12 @@
+import kotlin.test.*
+
+
+
+fun box() {
+    assertEquals("7FFF", 0x7FFF.toShort().toString(radix = 16).toUpperCase())
+    assertEquals("-8000", (-0x8000).toShort().toString(radix = 16))
+    assertEquals("-sfs", (-29180).toShort().toString(radix = 32))
+
+    assertFailsWith<IllegalArgumentException>("Expected to fail with radix 37") { 37.toShort().toString(radix = 37) }
+    assertFailsWith<IllegalArgumentException>("Expected to fail with radix 1") { 1.toShort().toString(radix = 1) }
+}