Switch to a new flow for advertising, sharing and joining worktrees

Now, when you open a local worktree, we immediately send an `OpenWorktree` message
to the server, telling it the name of the folder that you've opened, and the names of all the
collaborators (based on a `.zed.toml` file). The server responds with a unique id for the
worktree.

When starting share this local worktree, you now include this previously-assigned id
in the `ShareWorktree` message.

When joining a worktree, there is no longer a need to provide an access token. The access
is controlled by the set of "collaborator logins" that were provided when the worktree
was initially opened by the host.

zrpc/src/proto.rs

@@ -135,11 +135,13 @@ messages!(
     GetUsersResponse,
     JoinChannel,
     JoinChannelResponse,
+    JoinWorktree,
+    JoinWorktreeResponse,
     LeaveChannel,
     OpenBuffer,
     OpenBufferResponse,
-    JoinWorktree,
-    JoinWorktreeResponse,
+    OpenWorktree,
+    OpenWorktreeResponse,
     Ping,
     RemovePeer,
     SaveBuffer,
@@ -147,6 +149,7 @@ messages!(
     SendChannelMessageResponse,
     ShareWorktree,
     ShareWorktreeResponse,
+    UnshareWorktree,
     UpdateBuffer,
     UpdateWorktree,
 );
@@ -157,10 +160,12 @@ request_messages!(
     (JoinChannel, JoinChannelResponse),
     (OpenBuffer, OpenBufferResponse),
     (JoinWorktree, JoinWorktreeResponse),
+    (OpenWorktree, OpenWorktreeResponse),
     (Ping, Ack),
     (SaveBuffer, BufferSaved),
     (UpdateBuffer, Ack),
     (ShareWorktree, ShareWorktreeResponse),
+    (UnshareWorktree, Ack),
     (SendChannelMessage, SendChannelMessageResponse),
     (GetChannelMessages, GetChannelMessagesResponse),
 );
@@ -175,6 +180,7 @@ entity_messages!(
     JoinWorktree,
     RemovePeer,
     SaveBuffer,
+    UnshareWorktree,
     UpdateBuffer,
     UpdateWorktree,
 );