Add math expressions to grid setup
Description of the feature
By math I mean to be able to write operations like 472/4 in an input field. There is already several tools that support it, image stretch, canvas resize, selections... It would be an appreciated enhancement to also have it on grids.
Use cases
I think to have the grids cells to be a fraction of the image size is a very common use case of the grid tool if not the main.