Wider notifications on landscape lockscreen

Guarded by flag lockscreen.enable_landscape, skinny notifications are no longer used on small landscape screens so notifications will take up the full width of the notification stack. This is required for small landscape lockscreen feature.

Bug: 296571001
Bug: 293252410

Test: NotificationStackScrollLayoutTest
Change-Id: I469ab15eed507ef2c4e4d1b8c4d565dd44051a2f