Reorganize stdlib-js sources specific to the current JS backend

Move kotlin-stdlib-js project and the sources specific to the current backend to 'stdlib/js-v1' directory,
but leave sources that can be shared with the new IR backend in the common 'stdlib/js' location
with exception for 'stdlib/js/src/generated', which is used exclusively for current backend.
This simplifies sourceset configuration when building stdlib with the new backend.

libraries/stdlib/js/runtime/Enum.kt

@@ -1,27 +0,0 @@
-/*
- * Copyright 2010-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
- * that can be found in the license/LICENSE.txt file.
- */
-
-package kotlin
-
-public class Enum<T : Enum<T>> : Comparable<Enum<T>> {
-    @JsName("name$") private var _name: String = ""
-    @JsName("ordinal$") private var _ordinal: Int = 0
-
-    val name: String
-        get() = _name
-
-    val ordinal: Int
-        get() = _ordinal
-
-    override fun compareTo(other: Enum<T>) = ordinal.compareTo(other.ordinal)
-
-    override fun equals(other: Any?) = this === other
-
-    override fun hashCode(): Int = js("Kotlin.identityHashCode")(this)
-
-    override fun toString() = name
-
-    companion object
-}

libraries/stdlib/js/runtime/hacks.kt

@@ -1,16 +0,0 @@
-/*
- * Copyright 2010-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
- * that can be found in the license/LICENSE.txt file.
- */
-@file:Suppress("WRONG_EXTERNAL_DECLARATION")
-package kotlin.js
-
-import kotlin.annotation.AnnotationTarget.*
-
-@Retention(AnnotationRetention.BINARY)
-@Target(CLASS, FUNCTION, PROPERTY, CONSTRUCTOR, PROPERTY_GETTER, PROPERTY_SETTER)
-internal external annotation class JsName(val name: String)
-
-internal external annotation class native
-
-external fun js(code: String): dynamic