Handle SystemGestureRegion in TaskbarDragLayer

- Currently user can tap on taskbar icons when in persitent mode when a popup is visible on screen.
we are making it so that touch event is not performed at view level and get dismissed before at drag layer.

Test: Presubmit, Manual
Bug: 320229858
Flag: NONE
Change-Id: I9a76faa0e282317d808ba0f55b49741dc7b750a3