Add new variables / image attributes for megapixels and file size

[europlatus]

Feature request
Just a simple request to add variables and image attributes so we have more options for viewing and filtering, specifically related to image size.
Certain websites, print shops and other photographic services have a maximum/minimum megapixel count and/or file size, so the ability to view and filter by these criteria would be welcome.

We can currently view the image's width and height, so the megapixel count can be calculated, but it would be good to view this information without the need for a calculation, and there is no current option to filter via this information.

Proposed solution
Add all or some of these:

Variable: $(MEGAPIXELS.RAW)
Variable: $(MEGAPIXELS.EXPORT)
Variable: $(FILE.SIZE)
Image attribute: Megapixels (of image in its current state, i.e. after cropping if crop applied)
Image attribute: File size (original file on disk)

[Phemisters]

This looks similar to the ideas discussed in #19771 (comment) (Feature request - add $(FILE_SIZE) as variable)

As the file size is not currently stored in the darktable database, the suggestion there is to use a script to apply a tag. This might help you.