Add filedragover event to FileDrop Action Example#12

It would be nice for the [FileDrop Action Example](https://svelte.dev/repl/645841f327b8484093f94b84de8a7e64?version=3.41.0) to visually indicate the `filedragover` event. Maybe by changing border or background color. This would be especially useful if you have multiple `FileDrop` elements and `windowDrop=false`. With the visual indication the user knows for sure that s/he is dropping the file on an active element (and not just next to it). I tried to create a [FileDrop Action Example with visual filedragenter](https://svelte.dev/repl/8ea7d946137348d5ab294fdb9d649539?version=3.41.0) but the `filedragover` event is lost when the file is moved over the cloud image or text within the `FileDrop` element.