Adding ImageProvider.loadBuffer

Summary

Context

Description of change

Migration guide

Timeline

References

Summary

ImageProvider now has a method called loadBuffer that functions
 similarly to load, except that it decodes from an ui.ImmutableBuffer.

ui.ImmutableBuffer can now be created directly from an asset key.

The AssetBundle classes can now load an ui.ImmutableBuffer.

The PaintingBinding now has a method called
instantiateImageCodecFromBuffer, which functions similarly to
instantiateImageCodec.

ImageProvider.load is now deprecated, it will be removed in a future
 release.

PaintingBinding.instantiateImageCodec is now deprecated, it will be removed
 in a future release.

Context