feat(cropper): expand image export API

packages/cropper/docs/zh-Hans/examples/avatar-crop.mdx

@@ -10,31 +10,25 @@ toc:
 ## 示例 {#example}
 
 ```tsx
-import { Cropper, cropImage, type CropArea } from "@workspace/cropper"
+import { Cropper, type CropperHandle } from "@workspace/cropper"
 
 function AvatarCropper({ src }: { src: string }) {
-  const [area, setArea] = React.useState<CropArea>()
+  const cropperRef = React.useRef<CropperHandle>(null)
 
   async function saveAvatar() {
-    if (!area) return
-    const blob = await cropImage(src, area, {
+    const blob = await cropperRef.current?.getCropImage({
       height: 512,
       shape: "circle",
       type: "image/png",
       width: 512,
     })
-    await uploadAvatar(blob)
+    if (blob instanceof Blob) await uploadAvatar(blob)
   }
 
   return (
     <div className="space-y-4">
-      <Cropper
-        src={src}
-        shape="circle"
-        className="size-72"
-        onCropAreaChange={setArea}
-      />
-      <button type="button" disabled={!area} onClick={saveAvatar}>
+      <Cropper ref={cropperRef} src={src} shape="circle" className="size-72" />
+      <button type="button" onClick={saveAvatar}>
         保存头像
       </button>
     </div>