JS backend: compare enum entries strictly

#KT-7840 fixed

js/js.translator/testData/enum/cases/equals.kt

@@ -0,0 +1,20 @@
+package foo
+
+enum class Foo {
+    A,
+    B
+}
+
+fun box(): String {
+    testFalse { Foo.A == Foo.B }
+    testTrue { Foo.A != Foo.B }
+    testTrue { Foo.A == Foo.A }
+    testFalse { Foo.A != Foo.A }
+
+    testFalse { Foo.A == null }
+    testTrue { Foo.A != null }
+    testFalse { null == Foo.A }
+    testTrue { null != Foo.A }
+
+    return "OK"
+}