Move shared_buffers into BufferStore (#17020)

This also updates the SSH protocol (but not yet collab) to more closely
track which buffers are open on the client.

Release Notes:

- N/A

crates/proto/proto/zed.proto

@@ -278,7 +278,9 @@ message Envelope {
         LspExtSwitchSourceHeaderResponse lsp_ext_switch_source_header_response = 242;
 
         FindSearchCandidates find_search_candidates = 243;
-        FindSearchCandidatesResponse find_search_candidates_response = 244; // current max
+        FindSearchCandidatesResponse find_search_candidates_response = 244;
+
+        CloseBuffer close_buffer = 245; // current max
     }
 
     reserved 158 to 161;
@@ -870,6 +872,11 @@ message SaveBuffer {
     optional ProjectPath new_path = 4;
 }
 
+message CloseBuffer {
+    uint64 project_id = 1;
+    uint64 buffer_id = 2;
+}
+
 message ProjectPath {
     uint64 worktree_id = 1;
     string path = 2;

crates/proto/src/proto.rs

@@ -411,7 +411,8 @@ messages!(
     (AddWorktree, Foreground),
     (AddWorktreeResponse, Foreground),
     (FindSearchCandidates, Background),
-    (FindSearchCandidatesResponse, Background)
+    (FindSearchCandidatesResponse, Background),
+    (CloseBuffer, Foreground)
 );
 
 request_messages!(