Fix gallery controls popping in over content after presentation

Packages/GalleryVC/Sources/GalleryVC/GalleryPresentationAnimationController.swift

@@ -59,9 +59,17 @@ class GalleryPresentationAnimationController: NSObject, UIViewControllerAnimated
         let content = itemViewController.takeContent()
         content.view.translatesAutoresizingMaskIntoConstraints = true
         
-        container.addSubview(to.view)
+        // Use a separate dimming view from to.view, so that the gallery controls can be in front of the moving content.
-        container.addSubview(content.view)
+        let dimmingView = UIView()
+        dimmingView.backgroundColor = .black
+        dimmingView.frame = container.bounds
+        dimmingView.layer.opacity = 0
         
+        container.addSubview(dimmingView)
+        container.addSubview(content.view)
+        container.addSubview(to.view)
+
+        to.view.backgroundColor = nil
         to.view.layer.opacity = 0
         content.view.frame = sourceFrameInContainer
         content.view.layer.opacity = 0
@@ -77,6 +85,8 @@ class GalleryPresentationAnimationController: NSObject, UIViewControllerAnimated
         let animator = UIViewPropertyAnimator(duration: duration, timingParameters: spring)
         
         animator.addAnimations {
+            dimmingView.layer.opacity = 1
+            
             to.view.layer.opacity = 1
             
             content.view.frame = destFrameInContainer
@@ -90,6 +100,8 @@ class GalleryPresentationAnimationController: NSObject, UIViewControllerAnimated
         }
         
         animator.addCompletion { _ in
+            to.view.backgroundColor = .black
+            
             if sourceToDestTransform != nil {
                 self.sourceView.transform = origSourceTransform
             }