This PR adds a new event system based on the componentsAtPoint delivery mechanism. These events allow for a proper support of components that implement renderTree() method. The CameraComponent is one such component, with more planned in the future.
Additionally, the following improvements compared to the current tap events added:
- the same component can be tapped with multiple fingers simultaneously;
- a component that received onTapDown is guaranteed to receive onTapUp or onTapCancel later;
- a component that moves away from the point of touch will receive onTapCancel instead of onTapUp (even though the game widget receives onTapUp from Flutter).
Due to the fact that the switch from the current event system to the new event system is potentially a significant breaking change, the new event system is introduced as parallel to the existing one. This way we have more time to test the new system before recommending the switch and deprecating the old one; and the switch itself should feel more gradual.
