Improve gallery dismiss transition when source view is relatively small compared to content

See #520

Packages/GalleryVC/Sources/GalleryVC/GalleryDismissAnimationController.swift

@@ -47,8 +47,6 @@ class GalleryDismissAnimationController: NSObject, UIViewControllerAnimatedTrans
             container.addSubview(to.view)
         }
         
-        // This trick does not work as well here as it does for presentation, seemingly
-        // because the delayFactor:0.9 still results in the snapshot fading out too quickly :/
         let sourceSnapshot = sourceView.snapshotView(afterScreenUpdates: false)
         if let sourceSnapshot {
             let snapshotContainer = sourceView.ancestorForInsertingSnapshot
@@ -160,16 +158,21 @@ class GalleryDismissAnimationController: NSObject, UIViewControllerAnimatedTrans
             
             contentContainer.frame = sourceFrameInContainer
             content.view.frame = sourceSizeWithDestAspectRatioCenteredInContentContainer
-            content.view.layer.opacity = 0
             
             itemViewController.setControlsVisible(false, animated: false, dueToUserInteraction: false)
         }
         
+        // Delay fading out the content because if it's still big while it's semi-transparent,
+        // seeing the stuff behind it looks odd.
+        animator.addAnimations({
+            content.view.layer.opacity = 0
+        }, delayFactor: 0.35)
+        
         if let sourceSnapshot {
             animator.addAnimations({
                 self.sourceView.layer.opacity = 1
                 sourceSnapshot.layer.opacity = 0
-            }, delayFactor: 0.9)
+            }, delayFactor: 0.5)
         }
         
         animator.addCompletion { _ in