Move methods from TouchCursorInputMapperCommon.h into a cpp file

These methods are currently all used by two other files, but I want to
use one of them in TouchpadInputMapper.cpp. This means that I get
compilation errors saying the others are unused. Moving the method
definitions into a cpp file fixes this.

Bug: b/251196347
Test: builds without errors
Change-Id: Idc8b7bf2c8a1cb202e3122bcf5ff8552abbc9ca5