Update gesture navigation tutorial for foldable devices.

- Updated mock conversation layout to work on large devices.
- Added AnimatedTaskView helper view to animate previous task view.
- Added animation from single previous app to two peaking previous apps.
- Updated app orientation to work with larger screens (forced protrait was causing letterboxing).

Test: manual, tested tutorial on non-foldable device, foldable device (closed, opened in landscape, opened in portait and switching between the three)
Bug: 198434693
Bug: 187701213
Known issue: 200579260

Change-Id: I98cb269f7d25985989cf66e791bf535228ab5293