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/compatibility/dataClassEqualsHashCodeToString.kt

@@ -0,0 +1,13 @@
+// LANGUAGE_VERSION: 1.0
+
+data class Foo(val s: String)
+
+fun box(): String {
+    val f1 = Foo("OK")
+    val f2 = Foo("OK")
+    if (f1 != f2) return "Fail equals"
+    if (f1.hashCode() != f2.hashCode()) return "Fail hashCode"
+    if (f1.toString() != f2.toString() || f1.toString() != "Foo(s=OK)") return "Fail toString: $f1 $f2"
+
+    return f1.s
+}