Added support for UICollectionViewLayout Decoration View

[pookjw]

Old Style

import UIKit

class MyCollectionViewLayout: UICollectionViewCompositionalLayout {
    required init?(coder: NSCoder) {
        super.init { (section, layoutEnvironment) -> NSCollectionLayoutSection? in
            /* code */
        }

        let nib: UINib = .init(nibName: String(describing: MyCollectionReusableView.self), bundle: .main)
        register(nib, forDecorationViewOfKind: String(describing: MyCollectionReusableView.self))
    }
}

New Style

import UIKit
import Reusable

class MyCollectionViewLayout: UICollectionViewCompositionalLayout {
    required init?(coder: NSCoder) {
        super.init { (section, layoutEnvironment) -> NSCollectionLayoutSection? in
            /* code */
        }

        register(decorationViewType: MyCollectionReusableView.self)
    }
}