Update MousePadActivity.java to support doubletap drag
This MR is a continuation of !439 (closed) , which changes the default behavior of the remote mouse plugin's drag and drop trigger to be a double-tap to drag, and adds a new SwitchPreference that toggles between the old (hold to drag) and new behavior
Test Plan: Set double tap to drag as the drag and drop behavior, then drag with both touchpad and gyro-mouse
Set hold to drag as the drag and drop behavior, and confirm it still works