Hi,

Attached is a patch that adds support for an outline default state in
Diff buffers.

One state makes only files and hunks headings visibles. Another one
outlines files with long hunks. A third value is proposed for users who
want to implement their own state.

My point is that, when I first review a changeset, I am trying to get an
overview of the changes; And files cumulating long hunks often don't
help for that matter.

Tell me if it's worth including in Emacs 29.