Image: support storing full image buffers for each undo step

Update image undo to store buffers for each step:

- Undo buffers share tiles to avoid using too much memory.
- Undo support for different sized buffers
  allowing operations such as crop or resize.
- Paint tiles have been split into separate API/storage.
- Painting speed wont be impacted significantly
  since storing the extra tiles is done after the stroke & only
  for the first undo step.

Resolves T61263, see D5939 for details.

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