JS: move expressions test to box tests

js/js.translator/testData/box/expression/identityEquals/identityEqualsMethod.kt

@@ -0,0 +1,21 @@
+package foo
+
+class X
+
+fun box(): String {
+    val a = X()
+    val b = X()
+    if (a !== a) return "a !== a"
+    if (a === b) return "X() === X()"
+    val c = a
+    if (c !== a) return "c = a; c !== a"
+
+    if (X() === a) return "X() === a"
+
+    val t = !(X() === a)
+    if (!t) return "t = !(X() === a); t == false"
+
+    val f = !!(X() === a)
+    if (f) return "f = !!(X() === null); f == true"
+    return "OK";
+}