Create prototype for TouchpadDebugView

The TouchpadDebugViewController manages the lifecycle of the
TouchpadDebugView, which provides visual debugging information for
touchpad devices. This controller listens for touchpad device additions
and removals and appropriately shows or hides the debug view in response.

Bug: 355451044
Bug: 286551975

Test: Verified that the linear view pops up only when both the feature
flag is turned on and the touchpad is connected.
Flag: com.android.hardware.input.touchpad_visualizer
Change-Id: Iabe19a291c94ef3376e85bf80a7b45c6b1da2cbd