project_panel: Add support for copy/paste between different worktrees (#15396)

Closes https://github.com/zed-industries/zed/issues/5362

Release Notes:

- Added a way to copy/cut-paste between different worktrees ([#5362](https://github.com/zed-industries/zed/issues/5362))

crates/collab/src/tests/integration_tests.rs

@@ -3178,7 +3178,7 @@ async fn test_fs_operations(
 
     project_b
         .update(cx_b, |project, cx| {
-            project.copy_entry(entry.id, Path::new("f.txt"), cx)
+            project.copy_entry(entry.id, None, Path::new("f.txt"), cx)
         })
         .await
         .unwrap()