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/main.rs

@@ -100,12 +100,12 @@ fn fail_to_open_window(e: anyhow::Error, _cx: &mut AppContext) {
     eprintln!(
         "Zed failed to open a window: {e:?}. See https://zed.dev/docs/linux for troubleshooting steps."
     );
-    #[cfg(not(target_os = "linux"))]
+    #[cfg(not(any(target_os = "linux", target_os = "freebsd")))]
     {
         process::exit(1);
     }
 
-    #[cfg(target_os = "linux")]
+    #[cfg(any(target_os = "linux", target_os = "freebsd"))]
     {
         use ashpd::desktop::notification::{Notification, NotificationProxy, Priority};
         _cx.spawn(|_cx| async move {
@@ -172,7 +172,7 @@ fn main() {
         if *db::ZED_STATELESS || *release_channel::RELEASE_CHANNEL == ReleaseChannel::Dev {
             false
         } else {
-            #[cfg(target_os = "linux")]
+            #[cfg(any(target_os = "linux", target_os = "freebsd"))]
             {
                 crate::zed::listen_for_cli_connections(open_listener.clone()).is_err()
             }
@@ -426,7 +426,7 @@ fn main() {
 
         load_embedded_fonts(cx);
 
-        #[cfg(target_os = "linux")]
+        #[cfg(any(target_os = "linux", target_os = "freebsd"))]
         crate::zed::linux_prompts::init(cx);
 
         app_state.languages.set_theme(cx.theme().clone());
@@ -942,7 +942,7 @@ fn init_logger() {
                     config_builder.set_time_offset(offset);
                 }
 
-                #[cfg(target_os = "linux")]
+                #[cfg(any(target_os = "linux", target_os = "freebsd"))]
                 {
                     config_builder.add_filter_ignore_str("zbus");
                     config_builder.add_filter_ignore_str("blade_graphics::hal::resource");