[Flexiglass] Update the y position of HUNs

Use the y position from the placeholder to place HUNs in the NSSL.

Bug: 339181697
Test: check if HUNs are displayed correctly in Gone, Shade, and QuickSettings
Test: atest StackScrollAlgorithmTest
Flag: com.android.systemui.scene_container

Change-Id: I407e0c598f3ca4365a1309e2d81e4e628002f4d5
8 files changed