Add collapse functionality to outline entries (#33490)

partly Closes #23075 

Release Notes:

- Now provides collapse and enables functionality to outline entries
- Add a new expand_outlines_with_depth setting to customize how deep the
tree is expanded by when a file is opened

part 2 is in #34164 

**Visual examples**

![image](https://github.com/user-attachments/assets/5dcdb83b-6e3e-4bfd-8ef4-76ae2ce4d3e6)

![image](https://github.com/user-attachments/assets/7b786a5a-1a8c-4f34-aaa5-4a8d0afa9668)

![image](https://github.com/user-attachments/assets/1817be06-ac71-4480-8f17-0bd862e913c8)

assets/settings/default.json

@@ -691,7 +691,10 @@
       // 5. Never show the scrollbar:
       //    "never"
       "show": null
-    }
+    },
+    // Default depth to expand outline items in the current file.
+    // Set to 0 to collapse all items that have children, 1 or higher to collapse items at that depth or deeper.
+    "expand_outlines_with_depth": 100
   },
   "collaboration_panel": {
     // Whether to show the collaboration panel button in the status bar.

crates/outline_panel/src/outline_panel_settings.rs

@@ -31,6 +31,7 @@ pub struct OutlinePanelSettings {
     pub auto_reveal_entries: bool,
     pub auto_fold_dirs: bool,
     pub scrollbar: ScrollbarSettings,
+    pub expand_outlines_with_depth: usize,
 }
 
 #[derive(Copy, Clone, Debug, Serialize, Deserialize, JsonSchema, PartialEq, Eq)]
@@ -105,6 +106,13 @@ pub struct OutlinePanelSettingsContent {
     pub indent_guides: Option<IndentGuidesSettingsContent>,
     /// Scrollbar-related settings
     pub scrollbar: Option<ScrollbarSettingsContent>,
+    /// Default depth to expand outline items in the current file.
+    /// The default depth to which outline entries are expanded on reveal.
+    /// - Set to 0 to collapse all items that have children
+    /// - Set to 1 or higher to collapse items at that depth or deeper
+    ///
+    /// Default: 100
+    pub expand_outlines_with_depth: Option<usize>,
 }
 
 impl Settings for OutlinePanelSettings {