Use unbatched inputeventreceiver, reduce touchslop

To ensure gesture navigation has sufficient time to intercept gestures,
use unbatched inputreceiver, meaning that input events will be processed
immediately rather than on vsync boundaries.

Also, reduce touch slop to ensure that interception happens before the
app starts to react to the gesture.

Fix provided by michaelwr@.

Note: if the device is slow (for example, still executing first-boot
instructions), then the symptom can still be reproduced. However, once
the performance is good, then the issue is no longer observed.

Bug: 130352502
Test: open google maps and swipe from right and left. observe that the
map doesn't start moving before the back gesture icon appears.

Change-Id: I0696509c7f1cb0a0d2450080e0b61e2218a01140