[Dual Shade] Move NotificationsShade to the Start side on large screens.

This doesn't move lockscreen content to account for this change; that
will happen in a follow-up CL.

Bug: 384704521
Test: Manually tested by opening and closing both the notifications
 shade and quick settings shade on a folded and unfolded device, and
 confirming that notifications are rendered on the start side while
 quick settings are rendered on the end side.
Flag: com.android.systemui.dual_shade
Change-Id: I84ff3d5061b0cbb44167c221ee92a30b2a473623