Warn users when selecting non-Direct Boot apps.

Certain apps like Phone, SMS, Emergency Info, and IME are critical
enough that they ideally need to be runnable before the device is
unlocked after a reboot.  Users can still pick non-Direct Boot aware
apps, but this change now warns users that the selected app won't be
runnable until after unlocking.

Bug: 27196876
Change-Id: I0498904d2f664fb41e8c1e6bb30d1cbf437cf4b9