Preserve --user-data-dir across restarts (#62022)

# Objective

Fixes #57701.

When Zed is launched with `--user-data-dir`, a Zed-initiated
restart—such as `workspace: clear trusted worktrees` or Restart to
Update—can relaunch Zed without that argument. The restarted process
then uses the default data directory instead of the directory selected
by the user.

## Solution

- Store the resolved custom data directory as GPUI restart arguments
alongside the existing optional restart executable path.
- Forward those arguments when relaunching on Linux, macOS, and Windows.
- Preserve argument boundaries and native `OsString` values, including
paths containing spaces.
- On Windows updates, carry the arguments through
`auto_update_helper.exe` when it launches the updated `Zed.exe`.

Normal launches without `--user-data-dir` continue to restart without
additional arguments. This does not attempt to preserve unrelated CLI
arguments or general launch state.

## Testing

- `cargo fmt --all -- --check`
- `cargo test -p gpui`
- `cargo test -p auto_update --features workspace/test-support`
- `cargo check -p auto_update_helper --tests --target
x86_64-pc-windows-msvc`
- `./script/clippy -p gpui -p gpui_macos -p auto_update -p zed`
- `./script/clippy -p auto_update_helper --target
x86_64-pc-windows-msvc`

The regression tests cover simultaneous restart executable and argument
forwarding, Windows paths containing spaces and trailing backslashes,
updater-helper argument parsing, and the final `Zed.exe` command.

Compilation and unit tests were run on macOS. Linux and Windows runtime
behavior was reviewed but not run locally. A full `gpui_windows`
cross-target check was attempted, but its `psm` dependency requires the
MSVC `lib.exe` tool, which is not available on this macOS host; the
standalone Windows updater helper and its tests compile successfully for
the Windows target.

## 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 (no UI changes)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

---

Release Notes:

- Fixed Zed forgetting an explicitly passed `--user-data-dir` argument
after restarting (e.g. clicking "Restart to Update")

---------

Co-authored-by: Tom Houlé <tom@tomhoule.com>

crates/gpui_linux/src/linux/platform.rs

@@ -285,7 +285,7 @@ impl<P: LinuxClient + 'static> Platform for LinuxPlatform<P> {
         self.inner.compositor_name()
     }
 
-    fn restart(&self, binary_path: Option<PathBuf>) {
+    fn restart(&self, binary_path: Option<PathBuf>, arguments: Vec<std::ffi::OsString>) {
         use std::os::unix::process::CommandExt as _;
 
         // get the process id of the current process
@@ -312,7 +312,9 @@ impl<P: LinuxClient + 'static> Platform for LinuxPlatform<P> {
                 sleep 0.1
             done
 
-            "$1"
+            app_path="$1"
+            shift
+            "$app_path" "$@"
             "#;
 
         #[allow(
@@ -325,6 +327,7 @@ impl<P: LinuxClient + 'static> Platform for LinuxPlatform<P> {
             .arg(script)
             .arg(&app_pid)
             .arg(&app_path)
+            .args(arguments)
             .process_group(0)
             .spawn();