JS: move expressions test to box tests

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

@@ -0,0 +1,10 @@
+package foo
+
+
+fun box(): String {
+    val a: Int? = 0
+
+    val result = (a!! + 3)
+    if (result != 3) return "fail: $result"
+    return "OK"
+}