SCM: Outgoing commit should have Undo Commit

[joaomoreno]

Testing #203075

It would be great to have an Undo Commit and have it appear in the context menu of outgoing commits.

• If the commit is the last one, it just does what Undo Last Commit does, we have this today.
• Otherwise, it rebases the commits such that the commit that was selected gets moved to the top, thus becoming the last. (see SCM: Support reordering outgoing commits #203315) Then, Undo Last Commit can run.

Furthermore, Git: Undo Commit... could be an F1 action which would first show all outgoing commits in a quick pick. Once the user picks a commit, the steps above would run.