Update notification layouts when overlays change.

- Use the overlay directories specified in the ApplicationInfo retrieved
from PackageManager. The resources directories cached in LoadedApk in
ActvityThread may contain stale values for remote applications.
- Clear StatusBarNotification#mContext when overlays change to ensure
that the Resources for remote Contexts are not stale. These Contexts
will be recreated in the subsequent AsyncInflationTask.

Bug: 120987987
Test: mp core sysuig; change theme using theme picker
Change-Id: I100d164facdd4208610ee6409dd3868d6f304712