This adds support for [git
worktrees](https://matklad.github.io/2024/07/25/git-worktrees.html). It
fixes the errors that show up (git blame not working) and actually adds
support for detecting git changes in a `.git` folder that's outside of
our path (and not even in the ancestor chain of our root path).
(While working on this we discovered that our `.gitignore` handling is
not 100% correct. For example: we do stop processing `.gitignore` files
once we found a `.git` repository and don't go further up the ancestors,
which is correct, but then we also don't take into account the
`excludesFile` that a user might have configured, see:
https://git-scm.com/docs/gitignore)
Closes https://github.com/zed-industries/zed/issues/19842
Closes https://github.com/zed-industries/zed/issues/4670
Release Notes:
- Added support for git worktrees. Zed can now open git worktrees and
the git status in them is correctly handled.
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Co-authored-by: Antonio <antonio@zed.dev>
Co-authored-by: Bennet <bennet@zed.dev>
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