Add --interactive option to rebase

[topher200]

stg rebase --interactive is a new tool which mirrors git rebase --interactive.

Using an editor --interactive lets the user reorder patches, squash patch chains, or delete individual patches.

Further instructions could be added but this seemed like a good base set. I've been using this locally and it helps execute certain sets of commands much faster! Tests are included.

[topher200]

It seems like the tests for Python 3.5 and 3.6 are broken due to no @dataclass. I'll need to implement a replacement.

Update: fixed!

[jpgrayson]

Thanks for implementing this feature. I'm suspect this will be valuable to many StGit users.

I've added a few review comments for you to consider, but I think this code is good enough as-is. Thank you also for writing tests!

[topher200]

Thank you also for writing tests!

The test suite is what drew me to write this as a first-class citizen in the first place! (as opposed to a separate script in contrib). Once I got the hang of the harnesses I found it very easy to use a TDD style for adding new features to rebase.

I'd love any feedback you have on how to clean up the tests. I went for verbosity over DRY whenever I was confused, which is great because it led to landing the feature quickly 😂. Happy to clean them up however you see fit.

One (potential) downside of the way the --interactive tests are currently architected is that we can only set fake-editor once. That means that if two editor windows are opened by a single command (easy to do: write a stg rebase --interactive which includes a squash instruction, example: 1), we don't have any control over that second editor (in this case, the squash). The git repo gets around this restriction by having two fake-editors and somehow using the second one for the squash, but I didn't go there. Instead I just wrote my tests such that the commit message of the squash patch isn't relevant to the test. I don't think it's a big deal, just something I wanted to mention.

I have a few test steps like this: stg delete $(stg series --all --noprefix --no-description) &&. I needed to delete all patches to reset my stack (mostly due to the editor issue above 😂). I'm surprised there wasn't a lib function to do this already -- feel free suggest an alternative way of refreshing the stack (or creating a new stack) in the middle of a suite of tests.