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/assistant/src/prompt_library.rs

@@ -3,7 +3,6 @@ use crate::{
     InlineAssist, InlineAssistant, LanguageModelRequest, LanguageModelRequestMessage, Role,
 };
 use anyhow::{anyhow, Result};
-use assistant_slash_command::SlashCommandRegistry;
 use chrono::{DateTime, Utc};
 use collections::{HashMap, HashSet};
 use editor::{actions::Tab, CurrentLineHighlight, Editor, EditorElement, EditorEvent, EditorStyle};
@@ -448,7 +447,6 @@ impl PromptLibrary {
             self.set_active_prompt(Some(prompt_id), cx);
         } else if let Some(prompt_metadata) = self.store.metadata(prompt_id) {
             let language_registry = self.language_registry.clone();
-            let commands = SlashCommandRegistry::global(cx);
             let prompt = self.store.load(prompt_id);
             self.pending_load = cx.spawn(|this, mut cx| async move {
                 let prompt = prompt.await;
@@ -477,7 +475,7 @@ impl PromptLibrary {
                             editor.set_use_modal_editing(false);
                             editor.set_current_line_highlight(Some(CurrentLineHighlight::None));
                             editor.set_completion_provider(Box::new(
-                                SlashCommandCompletionProvider::new(commands, None, None),
+                                SlashCommandCompletionProvider::new(None, None),
                             ));
                             if focus {
                                 editor.focus(cx);