Introduce SHADE_LOCKED as a special state for the shade.

This state can be either reached by tapping the more card or dragging
down on any card. In this state, the shade is fully interactive, but
the phone is stil locked. This state can only be enterred if
redaction is off but security is on. If redaction is on, we will show
the bouncer instead and go to the normal shade.

Bug: 14161523
Change-Id: I95ca0991745ffc11ed1028581e3da15265c12ae5