uinput: add recording for simulating a touchpad connection

I was going to add this to some internal documentation, but realized
that it could also be useful for external contributors.

Bug: 355739040
Change-Id: Icc87633c29a0688c4842184aeb29c574c57ba8d6
Test: check touchpad settings appear after running
      $ adb shell uinput - < test-touchpad.evemu