Make triggers be bound to airdodge on non-gamecube controllers

## Summary
- Ignore soft-platform collision while an airborne fighter holds down.
- Preserve existing momentum and collision with solid floors.
- Add regression coverage for soft and solid platform behavior.

Reviewed-on: #65
Co-authored-by: Álex Román Núñez <eirexe@eirteam.moe>

src/input/mod.rs

@@ -116,13 +116,12 @@ impl Plugin for FighterInputPlugin {
                     binding: GamepadBinding::Button(GamepadButton::North),
                     action: InputMapAction::Jump,
                 },
-                // shield/airdodge -- both shoulder buttons, Melee-style
                 GamepadInputMapElement {
-                    binding: GamepadBinding::Button(GamepadButton::LeftTrigger),
+                    binding: GamepadBinding::Button(GamepadButton::LeftTrigger2),
                     action: InputMapAction::Shield,
                 },
                 GamepadInputMapElement {
-                    binding: GamepadBinding::Button(GamepadButton::RightTrigger),
+                    binding: GamepadBinding::Button(GamepadButton::RightTrigger2),
                     action: InputMapAction::Shield,
                 },
                 // attack