Do not serialize buffers containing bundled files (#38102)

Fix bundled file persistence by introducing SerializationMode enum

Closes: #38094

What's the issue?

Opening bundled files like Default Key Bindings
(zed://settings/keymap-default.json) was causing SQLite foreign key
constraint errors. The editor was trying to save state for these
read-only assets just like regular files, but since bundled files don't
have database entries, the foreign key constraint would fail.

The fix

Replaced the boolean serialize_dirty_buffers flag with a type-safe
SerializationMode enum:

```rust
pub enum SerializationMode {
    Enabled,   // Regular files persist across sessions
    Disabled,  // Bundled files don't persist
}
```

This prevents serialization at the source: workspace_id() returns None
for disabled editors, serialize() bails early, and should_serialize()
returns false. When opening bundled files, we set the mode to Disabled
from the start, so they're treated as transient views that never
interact with the persistence layer.

Changes

- editor.rs: Added SerializationMode enum and updated serialization
methods to respect it
- items.rs: Guarded should_serialize() to prevent disabled editors from
being serialized
- zed.rs: Set SerializationMode::Disabled in open_bundled_file()

Result

Bundled files open cleanly without SQLite errors and don't persist
across workspace reloads (expected behavior). Regular file persistence
remains unaffected.

Release Notes: Fixed SQLite foreign key constraint errors when opening
bundled files like Default Key Bindings.

---------

Co-authored-by: MrSubidubi <finn@zed.dev>

crates/editor/src/items.rs

@@ -1,7 +1,7 @@
 use crate::{
-    Anchor, Autoscroll, Editor, EditorEvent, EditorSettings, ExcerptId, ExcerptRange, FormatTarget,
-    MultiBuffer, MultiBufferSnapshot, NavigationData, ReportEditorEvent, SearchWithinRange,
-    SelectionEffects, ToPoint as _,
+    Anchor, Autoscroll, BufferSerialization, Editor, EditorEvent, EditorSettings, ExcerptId,
+    ExcerptRange, FormatTarget, MultiBuffer, MultiBufferSnapshot, NavigationData,
+    ReportEditorEvent, SearchWithinRange, SelectionEffects, ToPoint as _,
     display_map::HighlightKey,
     editor_settings::SeedQuerySetting,
     persistence::{DB, SerializedEditor},
@@ -1256,17 +1256,15 @@ impl SerializableItem for Editor {
         window: &mut Window,
         cx: &mut Context<Self>,
     ) -> Option<Task<Result<()>>> {
-        if self.mode.is_minimap() {
-            return None;
-        }
-        let mut serialize_dirty_buffers = self.serialize_dirty_buffers;
-
+        let buffer_serialization = self.buffer_serialization?;
         let project = self.project.clone()?;
-        if project.read(cx).visible_worktrees(cx).next().is_none() {
+
+        let serialize_dirty_buffers = match buffer_serialization {
             // If we don't have a worktree, we don't serialize, because
             // projects without worktrees aren't deserialized.
-            serialize_dirty_buffers = false;
-        }
+            BufferSerialization::All => project.read(cx).visible_worktrees(cx).next().is_some(),
+            BufferSerialization::NonDirtyBuffers => false,
+        };
 
         if closing && !serialize_dirty_buffers {
             return None;
@@ -1323,10 +1321,11 @@ impl SerializableItem for Editor {
     }
 
     fn should_serialize(&self, event: &Self::Event) -> bool {
-        matches!(
-            event,
-            EditorEvent::Saved | EditorEvent::DirtyChanged | EditorEvent::BufferEdited
-        )
+        self.should_serialize_buffer()
+            && matches!(
+                event,
+                EditorEvent::Saved | EditorEvent::DirtyChanged | EditorEvent::BufferEdited
+            )
     }
 }