Use current alpha on PRIMARY_BOUNCER->LOCKSCREEN

This prevents a flicker if the user swipes up but then swipes
down right after.

Fixes: 359842276
Test: atest PrimaryBouncerToLockscreenTransitionViewModelTest
Flag: com.android.systemui.migrate_clocks_to_blueprint
Change-Id: I3d2a028532ae7ecc6a89d31fd154dead16687a79
4 files changed