Incorporate Bayes into Falsing.

This uses the HistoryTracker on pin-based input to determine if a
tap outside of an intended region is a false touch, retracting the
pin input if we believe pocket dialing is occuring.

To do this, the cl properly integrates the HistoryTracker into
falsing, at least for single taps.

Most importantly, HistoryTracker#falsingBelief now return 0.5 when
it is unsure if a tap is false or not, and tends towards 0 when it
believes it's valid and 1 when it believes it's false.
HistoryTracker#falsingConfidence remains unchanged.

Test: atest SystemUITests && manual
Bug: 172655679
Change-Id: Ie771b1bf8ac564af7ffb68e190772fff5c562e89