Optimizing AccessibilityNodeInfo caching.

1. Before we were firing an accessibility event from the common
   predecessor of views with accessibility related state changes
   every X amount of time. These events designate that the tree
   rooted at the source is invalid and should not be cached.
   However, some of the state changes do not affect the view tree
   structure and we can just refresh the node instead of evicting
   and recaching nodes infos for views that did not change. Hence,
   we need a way to distinguish between a subtree changed over a
   node changed.

   Adding a new event type will not work since if say two siblings
   have local changes and their predecessor fires a window state
   change event, the client will drop the subtree rooted at the
   parent including the two views with changes. Subsequent, more
   specialized events emitted from the two changed siblings will
   be useless since the parent which did not changed is already
   evicted from the cache. Conversely, if the specialized events
   are fired from the two siblings with local changes and they
   are refreshed in the cache the subsequent window state change
   event from the common predecessor will force the refreshed
   nodes to be evicted.

   Hence, to enable distinction between node being changed and
   a subtree baing changed while not changing existing behavior,
   we will fire only window content change event with an additional
   argument specifying what changed - node or a subtree for now.
   Also if the changes are local to a view we fire the window
   content changed event from the view. So, the two siblings will
   fire such an event independently and the client will know that
   these are local changes and can just refresh the node. If the
   changes are structural, then we fire the window state change
   event from the common predecessor.

2. Added the input type of a text view as one of the properties
   reported by an AccessibilityNodeInfo. It is nice to prompt the
   user what input is expected.

3. Added a bundle for optional information to AccessiiblityNodeInfo.
   For example, it will be used for putting web specific properties
   that do not map cleanly to Android specific ones in WebView.

4. AccessibilityInteractionController was not taking into account
   whether the current accessibility focused node is shown before
   returing it. Hence, a disconnected node would be returned and
   caching it puts our cahche in an inconsistent state.

Change-Id: I8ed19cfb4a70bdd7597c3f105487f1651cffd9e0