Make particle animation state optional

[samme]

This change creates Phaser.GameObjects.Particles.Particle#anims only if the particle's emitter has at least one animation.

This should reduce memory usage and make cleanup faster (#6482, #6929) for games using non-animated particles.

It is a breaking change for games adding a first animation to the emitter after some particles have already been created. That will now cause an error. But the usual approach for adding animations will work like before:

this.add.particles(0, 0, 'explosion', {
  anim: ['explode']
  // ...
});

[photonstorm]

👍