Capture recent motion events used for falsing.

This spits out the last 20 motion events that the FalsingManager
uses into bug reports. It only records the data in eng/userdebug
builds.

This has been cleared with PWG over VC.

A tool to visualize this data in in progress.

Bug: 148084465
Test: manual
Change-Id: I3edf5dc8693a202ff0e31e737e912500a3e4363d