The recent introduction of PathList removed some of the ordering logic
resulting in paths always being alphabetised.

This change restores the previous logic for sorting worktrees in a
project using the newer PathList type.

Closes #39934

Release Notes:

- Fixed manual worktree reordering

<details>

<summary>Screen recording of it retaining the order</summary>


https://github.com/user-attachments/assets/0197d118-6ea7-4d2d-8fec-c917fcb9d277

</details>

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Co-authored-by: MrSubidubi <finn@zed.dev>