Fix drag reordering on mobile.

Auto-scrolling now scrolls a column at a time in order to provide a more
consistent scrolling experience. This fixes issues with dragging where
auto-scrolling happens too quickly to be useful.

Bug: 395227190
Test: Manually by drag reordering on both mobile and table. Also tested
dragging from the widget picker.
Flag: com.android.systemui.glanceable_hub_v2

Change-Id: I9959d21a8726abaac6aff74f86873de3c8a5665f