Add ability to copy & paste images that are in uploading state.

[Mati365]

Suggested merge commit message (convention)

Fix (image): Copying and pasting images in the uploading state is now possible. Closes #16967

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Additional information

It looks like we forgot to dump images that contain uploadId to clipboard data. It resulted in blank img being exported to the HTML:

I added a converter that lookups in file repository and checks if there is matching uploadId entry containing data. If so, it stores base64 of loaded image in src of img element, which is already pretty well handled later on.

Easily reproducible on http://localhost:8125/ckeditor5-image/tests/manual/imageupload.html

Before

before-image-upload-fix-2024-10-25_12.58.54.mp4

After

after-image-upload-fix-2024-10-25_12.55.59.mp4

[arkflpc]

After upload is done, will the copied image have src updated to the target or stick to the data-url?

[Mati365]

@arkflpc It's updated to the target, as uploadId is no longer present in downcast after successful uploading of image.

[arkflpc]

LGTM
@niegowski , wdyt?

[juliaflejterska]

@Mati365 We've finished testing the PR with @kubaklatt - it fixes the issue and looks good to us 👍

[niegowski]

If you trigger editor.getData() while an image is not fully uploaded, the editor data would contain the data: URL. For the user, it would look like the image is successfully uploaded but the URL would not point to the real asset on the server.
The proposed solution restarts the upload after the drop, but we should just keep the uploadId so the loader can match the given element and continue uploading.

[Mati365]

but we should just keep the uploadId

@niegowski we cannot, as it'll be no longer possible to paste such image to another instance of the editor. The second thing is that uploadId will be no longer valid after successful upload of original image, as it's removed from registry to avoid mem leak.

[Mati365]

@juliaflejterska / @charlttsie We changed a bit the behavior of this fix, so large data:base64 payload is no longer present in editor.getData and it's no longer possible to copy & paste such element from editor A, editor B (it'll work exactly like it is on production right now). Can you check it again?