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/enum/simple.kt

@@ -0,0 +1,12 @@
+enum class Season {
+    WINTER,
+    SPRING,
+    SUMMER,
+    AUTUMN
+}
+
+fun foo(): Season = Season.SPRING
+
+fun box() =
+    if (foo() == Season.SPRING) "OK"
+    else "fail"