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>

crates/worktree/src/worktree.rs

@@ -2079,7 +2079,7 @@ impl Snapshot {
             .map(|entry| &entry.path)
     }
 
-    fn child_entries<'a>(&'a self, parent_path: &'a Path) -> ChildEntriesIter<'a> {
+    pub fn child_entries<'a>(&'a self, parent_path: &'a Path) -> ChildEntriesIter<'a> {
         let mut cursor = self.entries_by_path.cursor();
         cursor.seek(&TraversalTarget::Path(parent_path), Bias::Right, &());
         let traversal = Traversal {
@@ -4706,7 +4706,7 @@ impl<'a, 'b> SeekTarget<'a, EntrySummary, (TraversalProgress<'a>, GitStatuses)>
     }
 }
 
-struct ChildEntriesIter<'a> {
+pub struct ChildEntriesIter<'a> {
     parent_path: &'a Path,
     traversal: Traversal<'a>,
 }