backend/tests: Add blackbox tests from Kotlin JVM

Added tests from testData/codegen/box directory. There are blackbox tests
in other directories and they are to be added.

backend.native/tests/external/codegen/blackbox/localClasses/localClassCaptureExtensionReceiver.kt

@@ -0,0 +1,14 @@
+class Outer {
+    fun String.id(): String {
+        class Local(unused: Long) {
+            fun result() = this@id
+            fun outer() = this@Outer
+        }
+
+        return Local(42L).result()
+    }
+
+    fun result(): String = "OK".id()
+}
+
+fun box() = Outer().result()