Guarding the touchpad visualiser window with the flag and settings

Guarded both the touchpad showDebugView and hideDebugView with both the touchpad visualizer flag and its developer option value in which both of them needs to be enabled in order to show the touchpad visualizer window.

Test: $ atest TouchpadDebugViewControllerTests.java
Test: Manual testing by flashing device and connecting the touchpad to see if the visualizer window will appear in both the cases when the toggle is enabled and when it is disabled
Bug: 359801523
Bug: 359212358
Flag: com.android.hardware.input.touchpad_visualizer
Change-Id: I6634a98f1af22175023fb474128514ced10a671c