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/StringTest/startsWithString.kt

@@ -0,0 +1,17 @@
+import kotlin.test.*
+
+
+
+fun box() {
+    assertTrue("abcd".startsWith("ab"))
+    assertTrue("abcd".startsWith("abcd"))
+    assertTrue("abcd".startsWith("a"))
+    assertFalse("abcd".startsWith("abcde"))
+    assertFalse("abcd".startsWith("b"))
+    assertFalse("".startsWith("a"))
+    assertTrue("some".startsWith(""))
+    assertTrue("".startsWith(""))
+
+    assertFalse("abcd".startsWith("aB", ignoreCase = false))
+    assertTrue("abcd".startsWith("aB", ignoreCase = true))
+}