[DO NOT MERGE] Use correct touch slop value for two-finger passthrough.

Throughout the gesture system we scale the touch slop radius to the number of fingers that are down at any given moment. Therefore the correct value to
trigger two-finger passthrough should be 2 * mTouchSlop.
This should make three-finger taps less problematic.
Bug: 163438921
Bug: 162521649
Test: manual
Change-Id: I4b36b5575bf11ad767d83effd6292dc84eadb27d
Change-Id: I9fb9d58ef679151c9fc595bcb375f6209ea3a5af

Change-Id: Ibcae2a5a3fde37b97859165efabf2b0df13ded9b