Add basic launch time prediction.

We estimate the next app launch time by looking at the past 7 days of
usage history and assuming that the user opens the app like clockwork.
If there is at least 24 hours of usage events, then we take the earliest
ACTIVITY_RESUMED event and estimate that the app will be launched
exactly 7 days after that event. If there is less than 24 hours of
history (which would be the case for a new app), then we take the
earliest ACTIVITY_RESUMED and add 24 hours. If we don't see any launch
event in the past 7 days, then we just say the app should be launched
within a year. If we have a long estimate for an app and it is launched,
then we re-evaluate our estimate because we can now estimate a launch
within the next 7 days.

Bug: 194532703
Test: atest FrameworksMockingServicesTests:PrefetchControllerTest
Test: manually launch apps and check dumpsys for expected launch time changes
Change-Id: I9ef5fc3e3df3c2d029243b1fb8949a4bf21900db