When the image viewer reloads an image after the underlying file
changes, it now tracks the `RenderImage` currently displayed by the view
and drops that image’s atlas entry before replacing it with a newly
decoded render image. This prevents rapidly updated images from
accumulating atlas textures per reload while keeping cleanup scoped to
the window that displayed the image.

Closes #35894

Release Notes:

- Fixed a memory leak when previewing images that are repeatedly updated
on disk.

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Co-authored-by: Smit Barmase <heysmitbarmase@gmail.com>