[flexiglass] Fix bouncer to lockscreen transition

Utilizes the scrim fade behavior that was already added for the shade -> lockscreen transition

Bug: 347773206
Test: manually verified transition follows spec (legacy)
Flag: com.android.systemui.scene_container
Change-Id: I14b38827cc6c1fe03e17aab9be53a24135b2d0ed
2 files changed