Address several autofix output issues by adding per-file line/column offset tracking

[finnigja]

This change addresses several autofix-related issues by adding per-file line/column offset tracking, and using those offsets when making edits to files.

There is no change in usage or documentation; it just addresses several edge cases within the existing autofix implementation (multi-line fixes, multiple-fixes-in-one-line fixes) that were not cleanly handled until now.

This should address several open issues; #4428, #3577, and #3388.

It adds several new e2e tests with rules/targets based on the issues above, and passes the existing tests in tests/e2e/test_autofix.py on my local machine.

PR checklist:

• Documentation is up-to-date
• Changelog is up-to-date
• Change has no security implications (otherwise, ping security team)

[CLAassistant]

All committers have signed the CLA.

[ievans]

@chair6 thanks for a terrific first contribution. This looks good to me. I think a docstring in code about what FileOffsets represents might be helpful, as it wasn't obvious to me at first, but as I understand it maintains the state the is necessary to track maintain correct behavior when applying multiple fixes to a single file/line.

[finnigja]

Thanks for the review, @ievans! Yup, you got it.. I've added the docstring.

[emjin]

This looks awesome! Made a very minor clarification to your comment. Also, I believe this won't work if two rules make a change to the same line, so we should just make a note of that.

Thank you so much for this contribution! A huge improvement for autofix