Fix Data Saver page crashed when rotate

This is because before fix mLoadAppRunnable is async run. And the
getContext() within it will return null when the Fragment in some not
ready lifecycle.

Use viewLifecycleOwner.lifecycleScope.launch to ensure the async
function will only be run when the view is ready, and automatically
canceled when out of scope.

Since this requires Kotlin Coroutine so migrate DataSaverSummary to
Kotlin, other functionality are keep no change.

Fix: 279863347
Test: Manual
Change-Id: I2e97a071c103e63b3306b801fc38f4704e3be0d2