Closes https://github.com/zed-industries/zed/issues/62801

# Objective

Fix issue https://github.com/flathub/dev.zed.Zed/issues/395 (reported
against the flathub package, but as described in it, it was introduced
by https://github.com/zed-industries/zed/pull/57440 ).

The symptom was that when running `flatpak run dev.zed.Zed <project
path>` (or some alias), then you'd get two "files" opened `--zed` and
`zed-editor`, with `zed-editor` also being added to the Zed project list
in the open window, which was quite annoying.

## Solution

- The flatpak CLI launcher, which self-launches with potential extra
arguments, now puts those arguments first rather than last.

## Testing

- A simple unit test targets the helper function that adds the arguments
- It also verifies that the parsed args come out as expected

## Self-Review Checklist:

- [ x ] I've reviewed my own diff for quality, security, and reliability
- [ x ] Unsafe blocks (if any) have justifying comments
- [ x ] The content adheres to Zed's UI standards
([UX/UI](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
and
[icon](https://github.com/zed-industries/zed/blob/main/crates/icons/README.md)
guidelines)
- [ x ] Tests cover the new/changed behavior
- [ x ] Performance impact has been considered and is acceptable

Note: I believe that other bullets than self-review and tests are not
relevant, as there is no unsafe, no expected performance impact, and no
UI changes.

---

Release Notes:

- Fixed an issue where Flatpak CLI launches would open
unrelated/nonexistent files due to a bug in argument construction

Co-authored-by: Kirill Bulatov <kirill@zed.dev>