Add callback to get notified of particle system changes

[DanielMartinus]

OnParticleSystemUpdateListener will become available when merged.

Implementation

viewKonfetti.onParticleSystemUpdateListener = object : OnParticleSystemUpdateListener {
    override fun onParticleSystemStarted(view: KonfettiView, system: ParticleSystem, activeSystems: Int) {
        // Particle system started
    }

    override fun onParticleSystemEnded(view: KonfettiView, system: ParticleSystem, activeSystems: Int) {
        // Particle system ended
    }
}