DiffCollection and Diff can be collapse

Paco Guzmanrequested to merge
diff-collection-collapse into master

DiffCollection we collapse from the safe number of files/lines, until what hard limit of files/lines was declared on instantiation.

The collapsed files count on the stats but we remove the raw data because won’t be shown.

Relates https://gitlab.com/gitlab-org/gitlab-ce/issues/19820 and https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4990

Based in this comment

Merge request reports