Fix item closing overly triggering save dialogues (#21374)

Closes https://github.com/zed-industries/zed/issues/12029

Allows to introspect project items inside items more deeply, checking
them for being dirty.
For that:
* renames `project::Item` into `project::ProjectItem`
* adds an `is_dirty(&self) -> bool` method to the renamed trait
* changes the closing logic to only care about dirty project items when
checking for save prompts conditions
* save prompts are raised only if the item is singleton without a
project path; or if the item has dirty project items that are not open
elsewhere

Release Notes:

- Fixed item closing overly triggering save dialogues

crates/repl/src/notebook/notebook_ui.rs

@@ -158,16 +158,6 @@ impl NotebookEditor {
         })
     }
 
-    fn is_dirty(&self, cx: &AppContext) -> bool {
-        self.cell_map.values().any(|cell| {
-            if let Cell::Code(code_cell) = cell {
-                code_cell.read(cx).is_dirty(cx)
-            } else {
-                false
-            }
-        })
-    }
-
     fn clear_outputs(&mut self, cx: &mut ViewContext<Self>) {
         for cell in self.cell_map.values() {
             if let Cell::Code(code_cell) = cell {
@@ -500,7 +490,7 @@ pub struct NotebookItem {
     id: ProjectEntryId,
 }
 
-impl project::Item for NotebookItem {
+impl project::ProjectItem for NotebookItem {
     fn try_open(
         project: &Model<Project>,
         path: &ProjectPath,
@@ -561,6 +551,10 @@ impl project::Item for NotebookItem {
     fn project_path(&self, _: &AppContext) -> Option<ProjectPath> {
         Some(self.project_path.clone())
     }
+
+    fn is_dirty(&self) -> bool {
+        false
+    }
 }
 
 impl NotebookItem {
@@ -656,7 +650,7 @@ impl Item for NotebookEditor {
     fn for_each_project_item(
         &self,
         cx: &AppContext,
-        f: &mut dyn FnMut(gpui::EntityId, &dyn project::Item),
+        f: &mut dyn FnMut(gpui::EntityId, &dyn project::ProjectItem),
     ) {
         f(self.notebook_item.entity_id(), self.notebook_item.read(cx))
     }
@@ -734,8 +728,13 @@ impl Item for NotebookEditor {
     }
 
     fn is_dirty(&self, cx: &AppContext) -> bool {
-        // self.is_dirty(cx) TODO
-        false
+        self.cell_map.values().any(|cell| {
+            if let Cell::Code(code_cell) = cell {
+                code_cell.read(cx).is_dirty(cx)
+            } else {
+                false
+            }
+        })
     }
 }