Add continuous falsing to keyguard.

With this change, taps outside of the bouncer inputs increase the
FalsingManager's belief that erroneous taps are happening. If the
belief becomes strong enough, the bouncer will be retracted.

Special attention is given to ensure that actual password inputs
are not recorded by the falsing manager. Valid button and pattern
inputs do not have their motion events recorded, but do _decrease_
the FalsingManager's belief in pocket dialing. Thus, a few bad taps
mixed with good taps will not retract the bouncer.

Test: atest SystemUITests && manual
Bug: 172655679
Change-Id: Iac8d2a2f41764f3c1cccb66b9d332c489cabca77