Adding methods to enable Touchpad Visualizer option

Adding methods to enable the Touchpad Visualizer option based on both the feature flag and the value of the settings toggle.

Test: atest TouchpadVisualizerPreferenceControllerTest
Test: Enable the flag and enable the "Show touchpad input" in developer
      options and trace the logs in TouchpadInputMapper.
Bug: 359801523
Flag: com.android.hardware.input.touchpad_visualizer
Change-Id: I1c51bc617e907081043cea3e6bab1c719f4d2df9