Allow transition between placeholder and loaded image to have an animation

[jaggernod]

Images fetched from the network can take significant time to load. Unfortunately, when a placeholder is defined and the remote asset is loaded we see an immediate switch (pop-in).

Could we provide animation for the transition or have a crossfade (with user-defined duration) between the placeholder and the final image?

The original flutter_svg already had this question posted.

P.S. Thank you for the package. It is really useful

[dnfield]

I'm open to this but doubt I will have time to work on it myself anytime soon.