Respect `image-dired-thumbnail-storage` variable to respect Thumbnail Managing Standard

[Thaodan]

Is your feature request related to a problem? Please describe.

Image-dired can reuse thumbnails created by other programs if image-dired-thumbnail-storage is set to standard or standard-large and alike.

If dirvish would do the same it could also reuse thumbnails and gain the performance benefit and reduce disk space usage by not using additional preview images

Describe the solution you'd like Respect the image-dired-thumbnail-storage variable and adjust the thumbnail functions to respect the thumbnail managing standard.

Describe alternatives you've considered Keep the current state.

Additional context

• Thumbnail Managing Standard Freedesktop.org spec

[alexluigit]

Thanks for the suggestion! The reason I use magick to generate thumbnails is that Emacs is struggled to display big images (in terms of file size) which in turn blocks UI. I'd love to make dirvish respect image-dired-thumbnail-storage if we can get around with this. I'll give it a try.