Use top relative layer for recents input

The swiping task for recents may contain multiple activities.
So the initial relative layer should consider the layer count.

Bug: 323192976
Test: Enter sub settings. Swipe up and scroll the Settings
      activity immediately. It should control the overview
      instead of the activity in overview.
Change-Id: Ic7c9ecf48eca8f358b879aaa7931adc1722618c1