Core Animation放大缩小；CAKeyframeAnimation

先放大1.2倍，再还原；两段动画时间比例为7:3；总时间0.4秒。整体效果现快后慢。

        let keyframeAnimation = CAKeyframeAnimation(keyPath: "transform.scale")//类型为缩放
        keyframeAnimation.keyTimes = [0, 0.7, 1.0]//整个动画的百分之几时进行修改
        keyframeAnimation.values = [0, 1.2, 1.0]//每个阶段的缩放比例，与keyTimes对应
        keyframeAnimation.duration = 0.4//动画持续时间
        keyframeAnimation.timingFunction = CAMediaTimingFunction(name: .easeOut)//整体效果要开始快结束慢
        animatorView.layer.add(keyframeAnimation, forKey: "pop")//动画的key为"pop"，以后可以通过这个key访问它