Add ability to open files with system default application (#17231)

crates/gpui/src/platform/test/platform.rs

@@ -318,6 +318,10 @@ impl Platform for TestPlatform {
     fn register_url_scheme(&self, _: &str) -> Task<anyhow::Result<()>> {
         unimplemented!()
     }
+
+    fn open_with_system(&self, _path: &Path) {
+        unimplemented!()
+    }
 }
 
 #[cfg(target_os = "windows")]