cubicweb-vcsfile #6354109 [sobjects] Add a diff service [validation pending]

This will be used in vcreview to display the diff between revisions of a given patch.

This can also be used within vcsfile in place of export-rev service, since we don't really need an exported patch (with header etc.).

prioritynormal
typebug
done in2.3.0
load left0.000
closed by#a73411748932 [sobjects] Add a service to compute the diff between revisions
patch[sobjects] Add a service to compute the diff between revisions [applied][sobjects] Add a service to compute the diff between revisions [folded][sobjects] Add a service to compute the diff between revisions [folded][sobjects] Add a service to compute the diff between revisions [folded]