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/kClassSimpleName.kt

@@ -0,0 +1,40 @@
+package foo
+
+class undefined
+
+class Outer {
+    class Nested
+
+    inner class Inner
+}
+
+fun testWithInstance() {
+    assertEquals("A", A()::class.simpleName)
+    assertEquals("B", B()::class.simpleName)
+    assertEquals("O", (O)::class.simpleName)
+    assertEquals("E", E.X::class.simpleName)
+    assertEquals("Y", E.Y::class.simpleName)
+// TODO uncomment after KT-13338 is fixed
+//    assertEquals("E", E.Z::class.simpleName)
+    assertEquals("undefined", undefined()::class.simpleName)
+    assertEquals("Nested", Outer.Nested()::class.simpleName)
+    assertEquals("Inner", Outer().Inner()::class.simpleName)
+}
+
+fun testWithClassReference() {
+    assertEquals("A", A::class.simpleName)
+    assertEquals("B", B::class.simpleName)
+    assertEquals("O", O::class.simpleName)
+    assertEquals("I", I::class.simpleName)
+    assertEquals("E", E::class.simpleName)
+    assertEquals("undefined", foo.undefined::class.simpleName)
+    assertEquals("Nested", Outer.Nested::class.simpleName)
+    assertEquals("Inner", Outer.Inner::class.simpleName)
+}
+
+fun box(): String {
+    testWithInstance()
+    testWithClassReference()
+
+    return "OK"
+}