I just updated to Unity 2019.3.0f1 from the beta, and “Gamepad” is no longer available in the binding dropdown:

“Listen” will also not detect Gamepad input.
I can bind to Gamepad by clicking the “T” and typing in the value I want.
Gamepad works fine in my game, and it shows up correctly in the input debugger, it’s just not available in this binding menu. Unplugging and plugging the gamepad back in did not help.