Way to read EXIF data from image, without downloading it twice?

## 🚀 Feature Requests

I need a way to read the EXIF data of an image, without having to download it twice from a URL.

I think this could be accomplished with a `DecoderCallback`, but I am not sure.

If not, could a mechanism please be added to intercept the raw fetched image bytes, before decoding, as a `Uint8List`, so that they can be fed to https://pub.dev/packages/exif ?

### Platforms affected (mark all that apply)
- [x] :iphone: iOS
- [x] :robot: Android