JS: move expressions test to box tests

js/js.translator/testData/box/expression/misc/elvis.kt

@@ -0,0 +1,21 @@
+package foo
+
+fun box(): String {
+    if (f(null) != false) {
+        return "fail1"
+    }
+    if (f(2) != true) {
+        return "fail2"
+    }
+    if (f(1) != false) {
+        return "fail3"
+    }
+    return "OK"
+}
+
+fun Int.isEven() = (this % 2) == 0
+
+fun f(a: Int?): Boolean {
+    return a?.isEven() ?: false
+
+}