T/ckeditor5/1985: Change how the temporary upload image is handled.

[jodator]

Suggested merge commit message (convention)

Fix: Image upload should handle images that are deeply nested in other blocks. Closes ckeditor/ckeditor5#1985.

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Additional information

• Rendering of the temporary image is done in a downcast conversion instead of listening on the doc.change event.
• Requires changes in:
  • upload plugin: T/ckeditor5/1985: add synchronous image data access ckeditor5-upload#99.
  • table plugin: T/209: Table cell post-fixer will refresh a cell only when it is needed. ckeditor5-table#212

[coveralls]

Coverage decreased (-0.3%) to 99.405% when pulling a3768e2 on t/ckeditor5/1985 into c3c0e4a on master.

[Reinmar]

Unfortunately, it does not work still:

[Reinmar]

Error:

[jodator]

Above mentioned bugs fixed with: ckeditor/ckeditor5-table#212. Anyway, we will need a follow-up with better upload checking so the upload (and cleanup) is not triggered more than once for the same image.

[Mgsy]

Now everything works fine 👌