[flexiglass] Lockscreen shortcuts are visible again.

It's not clear when lockscreen shortcuts stopped being visible in
Flexiglass but this CL fixes that problem.

The root cause is that KeyguardQuickAffordanceInteractor uses
isKeyguardShowing from KeyguardInteractor and that feeds on state that's
not being kept up-to-date when Flexiglass is on.

Fix: 335679293
Test: manually verified that the lockscreen shortcuts are visible and
can be long-pressed properly
Flag: ACONFIG com.android.systemui.scene_container DEVELOPMENT

Change-Id: I9106fcb1bebed2302db5646f4643c4f255eed88f