[Flexiglass] Update NSSL.updateStackPosition() to only update stack heights

NSSL.updateStackPosition() used to update AmbientState.mStackY, to scale it with the expansion fraction, but stackY is not used anymore with the SceneContainer.

Bug: 332574413
Test: check notification placement in various scenarios
Flag: com.android.systemui.scene_container
Change-Id: Ice2fe04118a1deb403bcd211c132a69bcbd2fc43
1 file changed