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/dataClasses/hashCode/float.kt

@@ -0,0 +1,7 @@
+data class A(val a: Float)
+
+fun box() : String {
+   val v1 = A(-10.toFloat()).hashCode()
+   val v2 = (-10.toFloat() as Float?)!!.hashCode()
+   return if( v1 == v2 ) "OK" else "$v1 $v2"
+}