[Android] React to activity state change within XWalkView

Previously, XWalkView relies on embedders to manage the
resource of XWalkView based on Activity lifecycle.

In this commit, implement XWalkView as ActivityStatusListener
and handle the lifecycle state change by itself.

BUG=
Thanks for your explanation. If `onActivityStateChange` can be exposed to the embedder, it would be better.

The pauseTimer/resumeTimer might be useful when the app want to do some network request background, it is by-design, and when the app is resumed, no time would be spent on resource loading, and so get a user experience improvement.

One thing may be paid attention to is, would the activity status change have conflict with onPause/onResume/onDestroy callback if for example, we call `XWalkView.onDestroy` in `onActivityStateChange` and also in `Activity.onDestroy`?