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/RegexTest/matchMultiline.kt

@@ -0,0 +1,10 @@
+import kotlin.text.*
+
+import kotlin.test.*
+
+
+fun box() {
+    val regex = "^[a-z]*$".toRegex(setOf(RegexOption.IGNORE_CASE, RegexOption.MULTILINE))
+    val matchedValues = regex.findAll("test\n\nLine").map { it.value }.toList()
+    assertEquals(listOf("test", "", "Line"), matchedValues)
+}