Add plumbing for touchpad settings

Also remove the tryTouchpadPointerSpeed method, since after discussion
on the touchpad settings design doc it turns out we don't need it.

Bug: 251196347, 247080509
Test: Use settings command in ADB shell to change values
Change-Id: Idcdeb6857f50c40e9a8231af135a24cc01920bc7
9 files changed