Add example and tests for ViewConfigurator

Tests/CollectionViewTests/ViewConfiguratorTests.swift

+import CustomDump
+import XCTest
+@testable import CollectionView
+
+// MARK: - Example view configurator:
+
+private class ProfileView: UIView {
+  let username = UILabel()
+}
+
+private struct User {
+  var name: String
+}
+
+private extension ViewConfigurator where View == ProfileView, Model == User {
+  static let profileViewUserConfigurator = ViewConfigurator { view, model in
+    view.username.text = model.name
+  }
+}
+
+// MARK: - Tests:
+
+final class ViewConfiguratorTests: XCTestCase {
+  func testExampleConfigurator() {
+    let profileView = ProfileView()
+    let user = User(name: "John")
+
+    let configure = ViewConfigurator.profileViewUserConfigurator
+    configure(profileView, with: user)
+
+    XCTAssertNoDifference(profileView.username.text, user.name)
+  }
+}