At least on the web, the cursor can be set at whatever scope we choose (e.g. entire window, flutter view element, etc). So in order for us to correctly scope the cursor, we would need the viewId information within the activateSystemCursor message.

At the moment, we are always setting the cursor property on the body element. It would be better to set the cursor property on all the <flutter-view> elements instead, for a few reasons:

1. Avoid polluting the cursor of other parts of the page that don't belong to Flutter.
2. Fix the mouse cursor when the Flutter View is moved to a PiP window (see comments below).