Add "Touchpad visualizer" to input developer options

Bug: 286551975
Bug: 350039816
Test: atest TouchpadVisualizerPreferenceControllerTest
Test: Manual testing using
      $ adb shell settings get system touchpad_visualizer
Flag: com.android.hardware.input.touchpad_visualizer

Change-Id: Ic5de704c49aabf1a80d202aa890055f7337d45d4