Add excerpts into outline panel (#13034)

Follow-up of https://github.com/zed-industries/zed/pull/12637

Adds excerpt items into the outline panel: now all outline items are
initially hidden under excerpt items that could be toggled open/closed
similar to directories.


![Screenshot 2024-06-14 at 10 45
04](https://github.com/zed-industries/zed/assets/2690773/9c9ef91b-1666-43c3-acc4-96f850098a28)

On active editor's selection change, a corresponding outline will be
revealed still, expanding the corresponding excerpt

![Screenshot 2024-06-14 at 10 45
13](https://github.com/zed-industries/zed/assets/2690773/7dfd14f7-4aca-48f2-8760-8e1362b9a043)

Release Notes:

- N/A

crates/editor/src/editor.rs

@@ -10888,14 +10888,14 @@ impl Editor {
             multi_buffer::Event::ExcerptsExpanded { ids } => {
                 cx.emit(EditorEvent::ExcerptsExpanded { ids: ids.clone() })
             }
-            multi_buffer::Event::Reparsed => {
+            multi_buffer::Event::Reparsed(buffer_id) => {
                 self.tasks_update_task = Some(self.refresh_runnables(cx));
 
-                cx.emit(EditorEvent::Reparsed);
+                cx.emit(EditorEvent::Reparsed(*buffer_id));
             }
-            multi_buffer::Event::LanguageChanged => {
+            multi_buffer::Event::LanguageChanged(buffer_id) => {
                 linked_editing_ranges::refresh_linked_ranges(self, cx);
-                cx.emit(EditorEvent::Reparsed);
+                cx.emit(EditorEvent::Reparsed(*buffer_id));
                 cx.notify();
             }
             multi_buffer::Event::DirtyChanged => cx.emit(EditorEvent::DirtyChanged),
@@ -11818,7 +11818,7 @@ pub enum EditorEvent {
     Edited {
         transaction_id: clock::Lamport,
     },
-    Reparsed,
+    Reparsed(BufferId),
     Focused,
     Blurred,
     DirtyChanged,

crates/editor/src/items.rs

@@ -903,7 +903,7 @@ impl Item for Editor {
                 f(ItemEvent::UpdateBreadcrumbs);
             }
 
-            EditorEvent::Reparsed => {
+            EditorEvent::Reparsed(_) => {
                 f(ItemEvent::UpdateBreadcrumbs);
             }