Input mocking is somewhat broken by Bevy 0.12

[alice-i-cecile]

          Did some more searching and I think I found the root of the problem! The issue is only with input mocking, or more specifically, sending inputs by events. Before the mentioned pr, `gamepad_button_event_system()` changed the `Axis<GamepadButton>` resource from events send by `bevy_gilrs`.

https://github.com/bevyengine/bevy/blob/756fb069b10c14bf06cc4ab07d0fce1e80fc559d/crates/bevy_input/src/gamepad.rs#L1178-L1211

https://github.com/bevyengine/bevy/blob/756fb069b10c14bf06cc4ab07d0fce1e80fc559d/crates/bevy_gilrs/src/gilrs_system.rs#L29C1-L35C4

After the pr, bevy_gilrs updates the resource directly and doesn't receive any bevy_input gamepad events, hence why input mocking for an axis button fails but the example works.

So now the only remaining question is, "what is the proper way to fix this?" Maybe reverse the part in the pr where reading EventReader<GamepadButtonChangedEvent> to set ResMut<Axis<GamepadButton>> in bevy_input was removed? I don't know how this would affect the changes from that pr though.

Originally posted by @100-TomatoJuice in #401 (comment)