最简单、最快捷的方法是使用UIImageView并对其进行快照：

extension UIImage {
    func resizedImage(targetSize: CGSize, contentMode: UIView.ContentMode) -> UIImage {
        let imgView = UIImageView(image: self)
        imgView.contentMode = contentMode
        imgView.frame = .init(origin: .zero, size: targetSize)
        return imgView.snapshot()
    }
}

extension UIView {
    func snapshot() -> UIImage {
        let format = UIGraphicsImageRendererFormat(for: .current)
        let renderer = UIGraphicsImageRenderer(bounds: bounds, format: format)
        return renderer.image { [self] context in
            layer.render(in: context.cgContext)
        }
    }
}