Fix undisposed PointerEvent JSObject on browser pointer move (#22112)

* Fix undisposed PointerEvent JSObject on browser pointer move

OnPointerMove dropped argsObj (the JSObject wrapping the native DOM
PointerEvent) without disposing it, except inside a Lazy factory only
evaluated when GetIntermediatePoints() is called - which doesn't happen
for ordinary moves/hover.

Without explicit Dispose(), release requires two steps: Mono GC must
collect the abandoned JSObject wrapper to release its JS handle, then
V8 can reclaim the underlying JS object. Verified with a standalone
FinalizationRegistry-based repro that Mono GC does not trigger on its
own under continuous pointermove-like allocation pressure, so undisposed
objects pile up - not a permanent leak though.

Fix by disposing argsObj in a finally block after routing, guaranteeing
deterministic release instead of depending on GC timing. Coalesced-event
resolution (GetCoalescedEvents) is unaffected since it only runs
synchronously within the same call when a consumer needs it.

* Updated comments

* Update src/Browser/Avalonia.Browser/BrowserInputHandler.cs

Co-authored-by: Max Katz <maxkatz6@outlook.com>

* Return empty list in lazy if argsObj has been disposed

---------

Co-authored-by: Max Katz <maxkatz6@outlook.com>

src/Browser/Avalonia.Browser/BrowserInputHandler.cs

@@ -79,10 +79,12 @@ internal class BrowserInputHandler
         {
             coalescedEvents = new Lazy<IReadOnlyList<RawPointerPoint>?>(() =>
             {
+                if (argsObj.IsDisposed)
+                    return [];
+
                 // To minimize JS interop usage, we resolve all points properties in a single call.
                 const int itemsPerPoint = 6;
                 var pointsProps = InputHelper.GetCoalescedEvents(argsObj);
-                argsObj.Dispose();
                 s_intermediatePointsPooledList.Clear();
 
                 var pointsCount = pointsProps.Length / itemsPerPoint;
@@ -101,8 +103,17 @@ internal class BrowserInputHandler
             });
         }
 
-        return RawPointerEvent(type, pointerType!, point, (RawInputModifiers)modifier, pointerId,
-            coalescedEvents);
+        try
+        {
+            return RawPointerEvent(type, pointerType!, point, (RawInputModifiers)modifier, pointerId,
+                coalescedEvents);
+        }
+        finally
+        {
+            // Release the JS handle after processing the event.
+            // ImmediatePoints is only expected to be accessed synchronously during event processing.
+            argsObj.Dispose();
+        }
     }
 
     public bool OnPointerDown(string pointerType, long pointerId, int buttons, double offsetX, double offsetY,