JS backend: basic support for class literals.

Added:
* the ability to get KClass using class literals (`::class`);
* the ability to get KClass from JsClass and vice versa;
* the ability to get simpleName.

 #KT-13345 Fixed

js/js.translator/testData/box/reflection/kClass.kt

@@ -0,0 +1,14 @@
+package foo
+
+fun box(): String {
+    check(A::class, A()::class)
+    check(B::class, B()::class)
+    check(O::class, (O)::class)
+    assertNotEquals(null, I::class)
+    check(E::class, E.X::class)
+    check(E::class, E.Y::class, shouldBeEqual = false)
+// TODO uncomment after KT-13338 is fixed
+//    check(E::class, E.Z::class)
+
+    return "OK"
+}