add test files

js/js.translator/testFiles/operatorOverloading/cases/plusOverload.kt

@@ -0,0 +1,12 @@
+package foo
+
+  class myInt(a : Int) {
+    val value = a;
+
+    fun plus(other : myInt) : myInt = myInt(value + other.value)
+  }
+
+fun box() : Boolean {
+
+  return (myInt(3) + myInt(5)).value == 8
+}