TAPL Increase size of Background to Overview swipe gesture

The instrumentation is using the swipe height, not width, for when in
landscape. Ideally this should be plumbed through but it isn't yet so fix
with a bigger gesture.

Test: TaplTestNexus#testBackground
Bug: 184059820
Change-Id: Id19f65f51468af707baea0a1b31569bb84f7fcb8