Encode axis_value in Variant for InputEvent::JOYSTICK_MOTION.
Encode axis_value in Variant for InputEvent::JOYSTICK_MOTION.

Fixes a bug that caused InputMap actions which have been set to joystick axes
not to work correctly on exported builds as the axis_value property wouldn't be serialized into engine.cfb.
See recent discussion in #49 (Post 121+)

quabug/godot,quabug/godot,quabug/godot,quabug/godot,quabug/godot,quabug/godot,quabug/godot,quabug/godot,quabug/godot,quabug/godot