Touchpad: add metric for tap dragging setting changes

Bug: 321978150
Bug: 324058706
Test: $ m statsd_testdrive
      $ ./out/host/linux-x86/bin/statsd_testdrive -e 97
      Then toggle the setting, press Enter in the terminal, and check
      the new actions are logged
Change-Id: I55b7cc3377e7b27e9570f3f1b79c1f300d5d5686