Prevent scrolling to top when expanding diff context

When clicking "show X hidden lines" on a pull request diff page, the view will jump to the top of the file. This can be annoying when dealing with large files as the user will often get displaced when reviewing the diff.

Previously to Bitbucket Server 7.0, it would expand the diff 10 lines at a time so it wouldn't scroll as much. However the current behavior doesn't scale well to large files with diffs in the middle/end of the file.

My suggestion is to remove the scrolling altogether.