spx: behavior of Sprite `die`

[nighca]

Ideally die should stop all behaviors of current sprite, which includes:

• Any event listening
• Any future code (?)
• Relationship with Game.Stop
• What about dying (when there is animation for dying)?

Now the coroutine will be aborted for cloned sprites, while not aborted for prototype sprites.

[nighca]

Related: goplus/spx#314, goplus/spx#315

[xushiwei]

In Scratch and SPX, the initial instance of a sprite is the prototype (somewhat similar to JavaScript). The prototype instance cannot be destroyed, so the 'die' function behaves differently for prototype instances and cloned instances.