[Feature request] Reverse region, hunk, file

[MarkRebane]

Is your feature request related to a problem? Please describe.

Magit has support for reversing regions, hunks, and files from existing commits. I've often found this feature useful in commit rewriting workflows that involve:

• reverse several small regions of code that found their way into the wrong commit
• make a fixup commit that removes the change from an unmerged commit
• make a fixup commit that re-adds the change to a different unmerged commit

Describe the solution you'd like

I'd like feature parity with Magit to reverse a region, hunk, or file, i.e.

• show a commit
• select a region with visual mode (or use the highlighted hunk / file)
• press 'u' to reverse the change
• reversing a change should:
  • create a staged change that undoes the region AND
  • create an unstaged change that reapplies the region

Additional context

Note that reversing a region is different to reverting a commit because:

• the scope of the reverse is smaller
• the output produces both the staged undo and unstaged redo

Screenshot of the outcome of reversing a visual region in Magit: