Factor tool definitions out of assistant (#21189)

This PR factors the tool definitions out of the `assistant` crate so
that they can be shared between `assistant` and `assistant2`.

`ToolWorkingSet` now lives in `assistant_tool`. The tool definitions
themselves live in `assistant_tools`, with the exception of the
`ContextServerTool`, which has been moved to the `context_server` crate.

As part of this refactoring I needed to extract the
`ContextServerSettings` to a separate `context_server_settings` crate so
that the `extension_host`—which is referenced by the `remote_server`—can
name the `ContextServerSettings` type without pulling in some undesired
dependencies.

Release Notes:

- N/A

crates/assistant/src/assistant_panel.rs

@@ -1,6 +1,5 @@
 use crate::slash_command::file_command::codeblock_fence_for_path;
 use crate::slash_command_working_set::SlashCommandWorkingSet;
-use crate::ToolWorkingSet;
 use crate::{
     assistant_settings::{AssistantDockPosition, AssistantSettings},
     humanize_token_count,
@@ -23,6 +22,7 @@ use crate::{
 };
 use anyhow::Result;
 use assistant_slash_command::{SlashCommand, SlashCommandOutputSection};
+use assistant_tool::ToolWorkingSet;
 use client::{proto, zed_urls, Client, Status};
 use collections::{hash_map, BTreeSet, HashMap, HashSet};
 use editor::{
@@ -1316,7 +1316,7 @@ impl AssistantPanel {
 
     fn restart_context_servers(
         workspace: &mut Workspace,
-        _action: &context_servers::Restart,
+        _action: &context_server::Restart,
         cx: &mut ViewContext<Workspace>,
     ) {
         let Some(assistant_panel) = workspace.panel::<AssistantPanel>(cx) else {