add parameters to in:fly (#14057)

Without a `y` value, `fly` is indistinguishable from `fade`

Author: Rich-Harris

documentation/docs/03-template-syntax/14-in-and-out.md

@@ -17,6 +17,6 @@ The `in:` and `out:` directives are identical to [`transition:`](transition), ex
 </label>
 
 {#if visible}
-	<div in:fly out:fade>flies in, fades out</div>
+	<div in:fly={{ y: 200 }} out:fade>flies in, fades out</div>
 {/if}
 ```