Limit home gesture distance to half of screen height

- Somehow when home gesture's travel distance is above certain number (~2560px in the bug's case), the touch will wrongly go to the 3P launcher instead of staying in quickstep launcehr only. As it's unusal for home gesture to be so long, limiting it to half of screen height.

Bug: 214279686
Test: presbumit and TaplTestsLauncher3#testWidgets on cf_tablet
Change-Id: I1107074556aea3011b186ba34dc830dbb1445517