Fix Auto folded dirs performance issues (#8556)

Fixed auto folded dirs which caused significant performance issues #8476
(#7674)

Moved from iterating over snapshot entries to use `child_entries`
function from `worktree.rs` by making it public

@maxbrunsfeld 

Release Notes:

- Fixed a bug where project panel settings changes would not be applied
immediately.
- Added a `project_panel.auto_fold_dirs` setting which collapses the
nesting in the project panel when there is a chain of folders containing
a single folder.
<img width="288" alt="Screenshot 2024-04-12 at 11 10 58 AM"
src="https://github.com/zed-industries/zed/assets/2280405/efd61e75-026c-464d-ba4d-90db5f68bad3">

---------

Co-authored-by: Mikayla <mikayla@zed.dev>

assets/settings/default.json

@@ -214,7 +214,10 @@
     // Whether to reveal it in the project panel automatically,
     // when a corresponding project entry becomes active.
     // Gitignored entries are never auto revealed.
-    "auto_reveal_entries": true
+    "auto_reveal_entries": true,
+    /// Whether to fold directories automatically
+    /// when a directory has only one directory inside.
+    "auto_fold_dirs": false
   },
   "collaboration_panel": {
     // Whether to show the collaboration panel button in the status bar.