[flexiglass] The active dot in the unlock pattern has a separate color.

Fix: 438750553
Test: Manually tested by opening the pattern bouncer, drawing a pattern
 and observing the dots. Tested with "Make pattern visible" setting
 turn on and off.
Flag: com.android.systemui.scene_container
Change-Id: Ibb0d065ef0da97daa3947eda062fd5ff71065352