Revert "Drop iOS 14 and macOS 11 support"

This reverts commit dcef7f47ff.

Shared/Player/Controls/ControlBackgroundModifier.swift

@@ -7,8 +7,19 @@ struct ControlBackgroundModifier: ViewModifier {
 
     func body(content: Content) -> some View {
         if enabled {
-            content
+            if #available(iOS 15, macOS 12, *) {
+                content
+                    .background(.thinMaterial)
+            } else {
+                content
+                #if os(macOS)
+                .background(VisualEffectBlur(material: .hudWindow))
+                #elseif os(iOS)
+                .background(VisualEffectBlur(blurStyle: .systemThinMaterial).edgesIgnoringSafeArea(edgesIgnoringSafeArea))
+                #else
                 .background(.thinMaterial)
+                #endif
+            }
         } else {
             content
         }

Shared/Player/Controls/PlayerControls.swift

@@ -255,6 +255,8 @@ struct PlayerControls: View {
             {
                 ThumbnailView(url: url)
                     .frame(maxWidth: .infinity, maxHeight: .infinity)
+                    .transition(.opacity)
+                    .animation(.default)
             } else if player.videoForDisplay == nil {
                 Color.black
             }