Add last time unhibernated to dumped info

Add the last time a package was unhibernated to app hibernation dump.
This can be used in bug reports or dumps to know that an app was
recently unhibernated.

Bug: 183142988
Test: adb shell dumpsys app_hibernation
Change-Id: I5bc1969d9385206b43e73b42d9d2067a66e9b609