Configure interactive dismissal of the Lock popup

On iPad, with a presentation style of .formSheet, the LockViewController
could be dismissed by simply tapping outside the bounds of the modal,
without regard for the `closable` [1] option.

Setting `isModalInPresentation` [2] based on `closable` allows controlling
whether or not UIKit should prevent the interactive dismissal of the popup.

[1] https://auth0.com/docs/libraries/lock-swift/lock-swift-configuration-options#closable
[2] https://developer.apple.com/documentation/uikit/uiviewcontroller/3229894-ismodalinpresentation

Lock/LockViewController.swift

@@ -44,6 +44,7 @@ public class LockViewController: UIViewController {
         lock.observerStore.controller = self
         if self.lock.style.modalPopup && UIDevice.current.userInterfaceIdiom == .pad {
             self.modalPresentationStyle = .formSheet
+            self.isModalInPresentation = !lock.options.closable
             self.preferredContentSize = CGSize(width: 375, height: 667)
         } else {
             self.modalPresentationStyle = .fullScreen