Improve Diff

[fcollonval]

Fixes #666

The diff components are back to pure Lumino widget. This suppresses the current complexity of putting non-react code (nbdime and codemirror) in react in lumino panel. And reduce code duplication with nbdime for easier maintenance.

The new structure use really the diff provider registry. And implementing file comparison with the new widget is easy (new internal command gitShowDiff that takes a DiffModel as argument).

TODO

• Fix styles
• [x] Connect settings and code mirror in plain text diff
• Add endpoint to compute nbdiff from two notebook content
• Implement refresh logic

This PR addresses also:

• Fixes Collapse all unchanged cells in Diff view #394
• Closes Pass ISettingsRegistry to Diff component #407
• Fixes Impossible to update an open diff #628
• Fixes Multiple diff are not shown #881
• Closes Update Diffs when the underlying file is changed #671

[github-actions]

👈 Launch a binder notebook on branch fcollonval/jupyterlab-git/fcollonval/issue666

[ianhi]

❤️ 🚀

[fcollonval]

@meeseeksdev backport to jlab-2

[lumberbot-app]

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

$ git checkout jlab-2
$ git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

$ git cherry-pick -m1 5a8df57afc360955ded077c9c078970feb1202fe

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

$ git commit -am 'Backport PR #900: Improve Diff'

4. Push to a named branch :

git push YOURFORK jlab-2:auto-backport-of-pr-900-on-jlab-2

5. Create a PR against branch jlab-2, I would have named this PR:

"Backport PR #900 on branch jlab-2"

And apply the correct labels and milestones.

Congratulation you did some good work ! Hopefully your backport PR will be tested by the continuous integration and merged soon!

If these instruction are inaccurate, feel free to suggest an improvement.