Add initial FreeBSD support (#20480)

This PR adds initial support for FreeBSD
(https://github.com/zed-industries/zed/issues/15309). While there is
still work left to be done, it seems to be usable. As discussed by
@syobocat (https://github.com/zed-industries/zed/discussions/10247), the
changes were just adding ```target_os = "freebsd"``` to wherever it
checks if the OS is Linux.


![image](https://github.com/user-attachments/assets/80ea5b29-047f-4cbd-8263-42e5fa6c94b7)

Needs to be build with ```RUSTFLAGS="-C link-dead-code"```

Known Issues:
- There's an issue in ```crates/project/src/environment.rs``` where a
command fails because ```/bin/sh``` on FreeBSD doesn't support the
```-l``` option.

![image](https://github.com/user-attachments/assets/c3c38633-160f-4f47-8840-e3da67f6ebc8)
- The file/folder choosers provided by the ```ashpd``` crate don't work
on FreeBSD (at least with KDE). This isn't that bad since a fallback
dialog is used.

![image](https://github.com/user-attachments/assets/29373006-1eb9-4ed0-bd52-2d0047fab418)
 - Moving to trash won't work.
- Numerous tests fail (when running on FreeBSD). While I haven't looked
into this much, it appears that the corresponding features seem to work
fine.

Release Notes:

- Added initial support for FreeBSD

crates/zed/src/zed.rs

@@ -1,6 +1,6 @@
 mod app_menus;
 pub mod inline_completion_registry;
-#[cfg(target_os = "linux")]
+#[cfg(any(target_os = "linux", target_os = "freebsd"))]
 pub(crate) mod linux_prompts;
 #[cfg(target_os = "macos")]
 pub(crate) mod mac_only_instance;
@@ -153,7 +153,7 @@ pub fn initialize_workspace(
         })
         .detach();
 
-        #[cfg(target_os = "linux")]
+        #[cfg(any(target_os = "linux", target_os = "freebsd"))]
         if let Err(e) = fs::linux_watcher::global(|_| {}) {
             let message = format!(db::indoc!{r#"
                 inotify_init returned {}
@@ -361,7 +361,7 @@ pub fn initialize_workspace(
             })
             .register_action(|_, _: &install_cli::Install, cx| {
                 cx.spawn(|workspace, mut cx| async move {
-                    if cfg!(target_os = "linux") {
+                    if cfg!(any(target_os = "linux", target_os = "freebsd")) {
                         let prompt = cx.prompt(
                             PromptLevel::Warning,
                             "CLI should already be installed",