JS: move more test to box tests

js/js.translator/testData/box/operatorOverloading/plusAndMinusAsAnExpression.kt

@@ -0,0 +1,13 @@
+package foo
+
+class A() {
+
+    operator fun unaryPlus() = "O"
+    operator fun unaryMinus() = "K"
+
+}
+
+fun box(): String {
+    var c = A()
+    return +c + -c
+}