Hide "Select" button while album chooser presented

TODO:

-[x] establish parent/child relation
-[x] reconcile changes with collection picker delegate
-[x] present/dismiss animation
-[x] animate title label
-[x] hide (some?) bar button items when collection picker presented

Nice to have:

-[] crop child view top - so that it comes *up to* the navbar bottom, but
    doesn't go behind

Signal/src/ViewControllers/PhotoLibrary/ImagePickerController.swift

@@ -317,6 +317,11 @@ class ImagePickerGridController: UICollectionViewController, PhotoLibraryDelegat
     }
 
     func updateSelectButton() {
+        guard !isShowingCollectionPickerController else {
+            navigationItem.rightBarButtonItem = nil
+            return
+        }
+
         let button = isInBatchSelectMode ? doneButton : selectButton
         button.tintColor = .ows_gray05
         navigationItem.rightBarButtonItem = button
@@ -389,6 +394,8 @@ class ImagePickerGridController: UICollectionViewController, PhotoLibraryDelegat
         UIView.animate(.promise, duration: 0.3, delay: 0, options: .curveEaseInOut) {
             collectionPickerView.superview?.layoutIfNeeded()
 
+            self.updateSelectButton()
+
             // *slightly* more than `pi` to ensure the chevron animates anti-clockwise
             let chevronRotationAngle = CGFloat.pi.nextUp
             self.titleIconView.transform = CGAffineTransform(rotationAngle: chevronRotationAngle)
@@ -405,6 +412,9 @@ class ImagePickerGridController: UICollectionViewController, PhotoLibraryDelegat
 
         UIView.animate(.promise, duration: 0.3, delay: 0, options: .curveEaseInOut) {
             collectionPickerController.view.frame = self.view.frame.offsetBy(dx: 0, dy: self.view.frame.height)
+
+            self.updateSelectButton()
+
             self.titleIconView.transform = .identity
         }.done { _ in
             collectionPickerController.view.removeFromSuperview()