It seems likely we will define a new "image decoder" interface that
returns `ListenableFuture<Bitmap>`, and naming that will be
hard/annoying if we need to keep this interface working too.
It's also not really clear what a non-test implementation of this
interface would be expected to do, since `DefaultImageDecoder` is
documented to always decode using `BitmapFactory`.
#minor-release
PiperOrigin-RevId: 569206325