[flexiglass] Adds keyguard_wm_state_refactor to flexi flags.

We need it to make KeyguardOcclusionInteractor work for Flexiglass
(which is in followup CL(s)).

Bug: 308001302
Test: verified that flexiglass can be turned on and off using
go/flexiglass-script after cl/615924471
Flag: ACONFIG com.android.systemui.scene_container DEVELOPMENT

Change-Id: Ic194d97ac5b4a3a03e1c97c5aa14f1d96c74b181