Downscale mask in mask editor for faster loading

### What problem are you experiencing?

When I open the mask editor with huge resolutions (between 4-8K) it takes a long time before the image loads in the mask editor. When you make your changes, it also takes a moment to save.

I'm proposing the option in comfy settings to downscale the mask into a smaller size for editing / creating the mask purposes. After editing, the mask would be resized to the original image's size.

┆Issue is synchronized with this [Notion page](https://www.notion.so/Issue-8737-Downscale-mask-in-mask-editor-for-faster-loading-3016d73d3650815e921ce2e3c72df41a) by [Unito](https://www.unito.io)