WPT details: The wpt test below checks for the presence of the event handler IDL attributes: https://wpt.fyi/results/gamepad/idlharness.window.html?label=experimental&label=master&aligned
Add ongamepadconnected and ongamepaddisconnected event handlers to the WindowEventHandlers interface mixin. This would enable support for window.ongamepad[dis]connected or document.body.ongamepad[dis]connected event handler attributes.
The gamepad[dis]connected events can be subscribed to using window.addEventListener() currently. This adds the ability to use window.ongamepad[dis]connected event handler attributes as well.