Improve typings for DragOverlay.

Better describe the function form to avoid consumers seeing errors like:
`  Type '(draggable: any) => Element' is not assignable to type 'FunctionElement'.ts(2322)`

For #56

Author: martinpengellyphillips

CHANGELOG.md

@@ -20,6 +20,8 @@
 
 - Don't apply redundant adjustment transformer when a drag overlay is used.
 
+- Improve typings for `DragOverlay` to better describe function form.
+
 ## [0.7.0] - 2022-09-07
 
 Refactor core to lean more into reactivity. Note there are multiple breaking

src/drag-overlay.tsx

@@ -1,11 +1,12 @@
 import { Portal } from "solid-js/web";
 import { JSX, ParentComponent, Show } from "solid-js";
 
-import { useDragDropContext } from "./drag-drop-context";
+import { Draggable, useDragDropContext } from "./drag-drop-context";
 import { transformStyle } from "./style";
 import { elementLayout } from "./layout";
 
 interface DragOverlayProps {
+  children: Element | ((activeDraggable: Draggable | null) => Element);
   class?: string;
   style?: JSX.CSSProperties;
 }