Get notification panel density from configuration instead of CentralSurfaces

This ensures that the density is correct also if the shade window is moved to another display.

In practise this fixes the scroll speed calculation when the shade is on another display.

Bug: 362719719
Test: NONE trivial bugfix
Flag: com.android.systemui.shade_window_goes_around
Change-Id: Iab31b400a16a97e028d15f25dd612adbdbc03d53