Show dropped image in output node

[bezo97]

Closes #497 feature request.

Implementation details:

• blob url and node id are optional parameters in loadGraphData
• sets the preview image on ~~all SaveImage nodes~~ the original node it was saved by
• using the output_node_id metadata when present
• works for any dropped png or webp, also from the queue
• PR does not include persistence of queue history

For reviewers:

1. Drop an image that contains workflow metadata with a SaveImage node
2. See dropped image in the node preview

[huchenlei]

See https://github.com/Comfy-Org/ComfyUI_frontend/issues/497#issuecomment-2397670656

This solution has a few missing parts:

• Only handles image output
• Only populte Preview Image and Save Image nodes
• Blindly populates all Preview Image and Save Image nodes

[bezo97]

Thanks for your review @huchenlei. Here's a task list based on the discussed:

• [ ] Save output node id in metadata: https://github.com/comfyanonymous/ComfyUI/pull/5235
• [x] Should work with any node, not just SaveImage and PreviewImage
• [x] Only populate the node it was saved by
• [ ] Handle audio output as well

Persisting the queue history would be a way bigger task so I'm going with your 2nd suggestion ("single asset that has workflow as metadata back to correct output node")

[huchenlei]

Closing for inactivity.