Update to lock task features API

1. Throw if notifications is given without home feature, as this
configuration allows potential escape routes.

2. Default power button menu to be on in order to be consistent with
existing lock task behaviour before P.

Bug: 71790952
Bug: 74381063
Test: manual
Change-Id: I2383c087a18739a158d55edcd84d22d1abdb887a
3 files changed