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/context_server/src/context_server.rs

@@ -0,0 +1,29 @@
+pub mod client;
+mod context_server_tool;
+mod extension_context_server;
+pub mod manager;
+pub mod protocol;
+mod registry;
+pub mod types;
+
+use command_palette_hooks::CommandPaletteFilter;
+pub use context_server_settings::{ContextServerSettings, ServerCommand, ServerConfig};
+use gpui::{actions, AppContext};
+
+pub use crate::context_server_tool::ContextServerTool;
+pub use crate::registry::ContextServerFactoryRegistry;
+
+actions!(context_servers, [Restart]);
+
+/// The namespace for the context servers actions.
+pub const CONTEXT_SERVERS_NAMESPACE: &'static str = "context_servers";
+
+pub fn init(cx: &mut AppContext) {
+    context_server_settings::init(cx);
+    ContextServerFactoryRegistry::default_global(cx);
+    extension_context_server::init(cx);
+
+    CommandPaletteFilter::update_global(cx, |filter, _cx| {
+        filter.hide_namespace(CONTEXT_SERVERS_NAMESPACE);
+    });
+}