Show the size of the files in image diff

Location：http：//git.xxx.com/xxx/merge_requests/xxx/diffs

Problem：In GitLab 10.8.3, file size information is shown in diff view while missing in 12.1.3.

Requirement：Would like to have file size back along with the dimension of images shown in the image diff. We have a lot of cases that the images are used as resources for mobile client application. It's needed to check if the file size matches the size requirement.