Prevent browser upscaling for responsive images

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.

Closes #3550869. Authored with an AI coding agent.

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