Enable a setting to decide whether to use pixel alpha in collision detection

[JiepengTan]

Enable a setting to decide whether to use pixel alpha in collision detection

By default, pixel-based collision detection is used (to stay consistent with Scratch).
Only when the project's index.json configuration property collisionByShape is set to true will the engine's collision box be used for collision detection.

eg: index.json

{
  "collisionByShape": true,
  ... other configs
}