Searchables aren't available until after the user is unlocked. We
could scan for them while locked, but we're aiming for a minimalist
environment, and scanning them while locked would require us to send
a changed broadcast on every boot.
Switch to using new SystemService lifecycle for faster event
delivery. Restore broken global search observer. Verified that
apps on external storage are handled correctly.
Bug: 26471205
Change-Id: Id99ffe2ea6db37a394454cc7dfa4eab10280ff35
4175be2f4e