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/project_panel/src/project_panel_settings.rs

@@ -4,14 +4,14 @@ use schemars::JsonSchema;
 use serde_derive::{Deserialize, Serialize};
 use settings::{Settings, SettingsSources};
 
-#[derive(Clone, Debug, Serialize, Deserialize, JsonSchema)]
+#[derive(Clone, Debug, Serialize, Deserialize, JsonSchema, Copy, PartialEq)]
 #[serde(rename_all = "snake_case")]
 pub enum ProjectPanelDockPosition {
     Left,
     Right,
 }
 
-#[derive(Deserialize, Debug)]
+#[derive(Deserialize, Debug, Clone, Copy, PartialEq)]
 pub struct ProjectPanelSettings {
     pub default_width: Pixels,
     pub dock: ProjectPanelDockPosition,
@@ -20,6 +20,7 @@ pub struct ProjectPanelSettings {
     pub git_status: bool,
     pub indent_size: f32,
     pub auto_reveal_entries: bool,
+    pub auto_fold_dirs: bool,
 }
 
 #[derive(Clone, Default, Serialize, Deserialize, JsonSchema, Debug)]
@@ -54,6 +55,11 @@ pub struct ProjectPanelSettingsContent {
     ///
     /// Default: true
     pub auto_reveal_entries: Option<bool>,
+    /// Whether to fold directories automatically
+    /// when directory has only one directory inside.
+    ///
+    /// Default: false
+    pub auto_fold_dirs: Option<bool>,
 }
 
 impl Settings for ProjectPanelSettings {