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/extensionFunctions/kt3646.kt

@@ -0,0 +1,14 @@
+// TODO: muted automatically, investigate should it be ran for JS or not
+// IGNORE_BACKEND: JS
+
+fun test(cl: Int.() -> Int):Int = 11.cl()
+
+class Foo {
+    val a = test { this }
+}
+
+fun box(): String {
+    if (Foo().a != 11) return "fail"
+
+    return "OK"
+}