JS: move expressions test to box tests

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

@@ -0,0 +1,12 @@
+package foo
+
+var c = 0
+val a: Int?
+    get() {
+        c++
+        return 2
+    }
+
+fun box(): String {
+    return if (c == 0 && (a!! + 3) == 5 && c == 1) return "OK" else "fail"
+}