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/matchIgnoreCase.kt

@@ -0,0 +1,9 @@
+import kotlin.text.*
+
+import kotlin.test.*
+
+
+fun box() {
+    for (input in listOf("ascii", "shrödinger"))
+        assertTrue(input.toUpperCase().matches(input.toLowerCase().toRegex(RegexOption.IGNORE_CASE)))
+}