Add skyx packages for all the Sky demos (except game)

sky/sdk/example/BUILD.gn

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 group("example") {
   testonly = true
 
   deps = []
 
   if (is_android) {
     deps += [
       "//sky/sdk/example/mine_digger",
+      "//sky/sdk/example/rendering",
       "//sky/sdk/example/stocks",
+      "//sky/sdk/example/widgets",
     ]
   }
 }