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/smartCasts/implicitMemberReceiver.kt

@@ -0,0 +1,20 @@
+open class A {
+    open val a = "OK"
+}
+
+class B : A() {
+    override val a = "FAIL"
+    fun foo() = "CRUSH"
+}
+
+class C {
+    fun A?.complex(): String {
+        if (this is B) return foo()
+        else if (this != null) return a
+        else return "???"
+    }
+
+    fun bar() = A().complex()
+}
+
+fun box() = C().bar()