feat(mobile): video zooming in asset viewer (#22036)

* wip

* Functional implementation, still need to bug test.

* Fixed flickering bugs

* Fixed bug with drag actions interfering with zoom panning. Fixed video being zoomable when bottom sheet is shown. Code cleanup.

* Add comments and simplify video controls

* Clearer variable name

* Fix bug where the redundant onTapDown would interfere with zooming gestures

* Fix zoom not working the second time when viewing a video.

* fix video of live photo retaining pan from photo portion

* code cleanup and simplified widget stack

---------

Co-authored-by: Alex <alex.tran1502@gmail.com>

mobile/lib/widgets/asset_viewer/center_play_button.dart

@@ -21,23 +21,20 @@ class CenterPlayButton extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    return ColoredBox(
-      color: Colors.transparent,
-      child: Center(
-        child: UnconstrainedBox(
-          child: AnimatedOpacity(
-            opacity: show ? 1.0 : 0.0,
-            duration: const Duration(milliseconds: 100),
-            child: DecoratedBox(
-              decoration: BoxDecoration(color: backgroundColor, shape: BoxShape.circle),
-              child: IconButton(
-                iconSize: 32,
-                padding: const EdgeInsets.all(12.0),
-                icon: isFinished
-                    ? Icon(Icons.replay, color: iconColor)
-                    : AnimatedPlayPause(color: iconColor, playing: isPlaying),
-                onPressed: onPressed,
-              ),
+    return Center(
+      child: UnconstrainedBox(
+        child: AnimatedOpacity(
+          opacity: show ? 1.0 : 0.0,
+          duration: const Duration(milliseconds: 100),
+          child: DecoratedBox(
+            decoration: BoxDecoration(color: backgroundColor, shape: BoxShape.circle),
+            child: IconButton(
+              iconSize: 32,
+              padding: const EdgeInsets.all(12.0),
+              icon: isFinished
+                  ? Icon(Icons.replay, color: iconColor)
+                  : AnimatedPlayPause(color: iconColor, playing: isPlaying),
+              onPressed: onPressed,
             ),
           ),
         ),