Lay the groundwork for collaborating on assistant panel (#13991)

This pull request introduces collaboration for the assistant panel by
turning `Context` into a CRDT. `ContextStore` is responsible for sending
and applying operations, as well as synchronizing missed changes while
the connection was lost.

Contexts are shared on a per-project basis, and only the host can share
them for now. Shared contexts can be accessed via the `History` tab in
the assistant panel.

<img width="1819" alt="image"
src="https://github.com/zed-industries/zed/assets/482957/c7ae46d2-cde3-4b03-b74a-6e9b1555c154">


Please note that this doesn't implement following yet, which is
scheduled for a subsequent pull request.

Release Notes:

- N/A

crates/project/src/project.rs

@@ -355,6 +355,9 @@ pub enum Event {
     },
     CollaboratorJoined(proto::PeerId),
     CollaboratorLeft(proto::PeerId),
+    HostReshared,
+    Reshared,
+    Rejoined,
     RefreshInlayHints,
     RevealInProjectPanel(ProjectEntryId),
     SnippetEdit(BufferId, Vec<(lsp::Range, Snippet)>),
@@ -1716,6 +1719,7 @@ impl Project {
         self.shared_buffers.clear();
         self.set_collaborators_from_proto(message.collaborators, cx)?;
         self.metadata_changed(cx);
+        cx.emit(Event::Reshared);
         Ok(())
     }
 
@@ -1753,6 +1757,7 @@ impl Project {
             .collect();
         self.enqueue_buffer_ordered_message(BufferOrderedMessage::Resync)
             .unwrap();
+        cx.emit(Event::Rejoined);
         cx.notify();
         Ok(())
     }
@@ -1805,9 +1810,11 @@ impl Project {
                 }
             }
 
-            self.client.send(proto::UnshareProject {
-                project_id: remote_id,
-            })?;
+            self.client
+                .send(proto::UnshareProject {
+                    project_id: remote_id,
+                })
+                .ok();
 
             Ok(())
         } else {
@@ -8810,6 +8817,7 @@ impl Project {
                     .retain(|_, buffer| !matches!(buffer, OpenBuffer::Operations(_)));
                 this.enqueue_buffer_ordered_message(BufferOrderedMessage::Resync)
                     .unwrap();
+                cx.emit(Event::HostReshared);
             }
 
             cx.emit(Event::CollaboratorUpdated {