Fix incorrect padding and multiline layer frame calculation

[yzhao198]

Summary

Thank you for writing this library. Here is a snippet of code I used when testing SkeletonView:

import UIKit
import SkeletonView

class ViewController: UIViewController {

    private lazy var label: UILabel = {
        let label = UILabel()
        label.translatesAutoresizingMaskIntoConstraints = false
        label.numberOfLines = 2
        label.skeletonLineSpacing = 8
        label.font = .systemFont(ofSize: 10)
        label.lastLineFillPercent = 50
        label.skeletonPaddingInsets = .init(top: 12, left: 0, bottom: 12, right: 30)
        label.isSkeletonable = true
        
        return label
    }()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        view.backgroundColor = .white
        
        SkeletonAppearance.default.multilineHeight = 12
        
        view.addSubview(label)
        
        label.heightAnchor.constraint(equalToConstant: 54).isActive = true
        label.widthAnchor.constraint(equalToConstant: 250).isActive = true
        label.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
        label.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true
        
        view.isSkeletonable = true
        view.showSkeleton()
    }
}

The desired result should be

but the current version (1.10.0) gives me

Given my testing device is NOT RTL, it is clear the padding is incorrectly rendered. After the changes made in this MR, the desired result is achieved.

Requirements (place an x in each of the [ ])

• I've read and understood the Contributing guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[Juanpe]

Hi @yzhao198, thanks for your first contribution. I've checked the code and it looks perfect.

There is only one thing to do before merging. You should update the CHANGELOG file including this PR, ok?

Thanks again

[yzhao198]

Thanks for your review @Juanpe I've updated CHANGELOG.md.

[Juanpe]

Looks nice! 👌🏼