fix: #3550869 Add next larger srcset candidate in canvas:image to prevent browser upscaling

Bálint Klérirequested to merge
issue/canvas-3550869:3550869-srcset-next-width into 1.x

Ensures canvas:image includes the next larger srcset candidate so browsers downscale instead of upscaling images.

Testing instructions

See issue description for test SDC: #3550869 (closed).

Closes #3550869 (closed). Authored with an AI coding agent.

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