设置按钮内容右对齐

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按钮UIButton 上的image,title等content右对齐

• 使用方法setContentHorizontalAlignment

[self.attentionBtn setContentHorizontalAlignment:UIControlContentHorizontalAlignmentRight];

• 下面三个方法无效,不要用

    self.attentionBtn.contentMode = UIViewContentModeRight;
    self.attentionBtn.contentMode = UIViewContentModeTopRight;
    self.attentionBtn.contentMode = UIViewContentModeBottomRight;

• 同样使用方法 setContentVerticalAlignment 实现上下对齐

枚举值：

typedef NS_ENUM(NSInteger, UIControlContentHorizontalAlignment) {
    UIControlContentHorizontalAlignmentCenter = 0,
    UIControlContentHorizontalAlignmentLeft   = 1,
    UIControlContentHorizontalAlignmentRight  = 2,
    UIControlContentHorizontalAlignmentFill   = 3,
    UIControlContentHorizontalAlignmentLeading  API_AVAILABLE(ios(11.0), tvos(11.0)) = 4,
    UIControlContentHorizontalAlignmentTrailing API_AVAILABLE(ios(11.0), tvos(11.0)) = 5,
};