Exclude TaskViews from system gestures

Test:
- Enter overview
- Swipe from right edge (no TaskView) goes back
- Swipe from left edge on top of TaskView scrolls to it
- Now swipe from either edge scrolls
- Swipe outside carousel goes back

Bug: 129297464
Change-Id: I0abd444a6e8d8daf79a824c94bdd05c01dfe19cb