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_settings/src/context_server_settings.rs

@@ -0,0 +1,61 @@
+use std::sync::Arc;
+
+use collections::HashMap;
+use gpui::AppContext;
+use schemars::gen::SchemaGenerator;
+use schemars::schema::{InstanceType, Schema, SchemaObject};
+use schemars::JsonSchema;
+use serde::{Deserialize, Serialize};
+use settings::{Settings, SettingsSources};
+
+pub fn init(cx: &mut AppContext) {
+    ContextServerSettings::register(cx);
+}
+
+#[derive(Deserialize, Serialize, Clone, PartialEq, Eq, JsonSchema, Debug, Default)]
+pub struct ServerConfig {
+    /// The command to run this context server.
+    ///
+    /// This will override the command set by an extension.
+    pub command: Option<ServerCommand>,
+    /// The settings for this context server.
+    ///
+    /// Consult the documentation for the context server to see what settings
+    /// are supported.
+    #[schemars(schema_with = "server_config_settings_json_schema")]
+    pub settings: Option<serde_json::Value>,
+}
+
+fn server_config_settings_json_schema(_generator: &mut SchemaGenerator) -> Schema {
+    Schema::Object(SchemaObject {
+        instance_type: Some(InstanceType::Object.into()),
+        ..Default::default()
+    })
+}
+
+#[derive(Deserialize, Serialize, Clone, PartialEq, Eq, JsonSchema, Debug)]
+pub struct ServerCommand {
+    pub path: String,
+    pub args: Vec<String>,
+    pub env: Option<HashMap<String, String>>,
+}
+
+#[derive(Deserialize, Serialize, Default, Clone, PartialEq, Eq, JsonSchema, Debug)]
+pub struct ContextServerSettings {
+    /// Settings for context servers used in the Assistant.
+    #[serde(default)]
+    pub context_servers: HashMap<Arc<str>, ServerConfig>,
+}
+
+impl Settings for ContextServerSettings {
+    const KEY: Option<&'static str> = None;
+
+    type FileContent = Self;
+
+    fn load(
+        sources: SettingsSources<Self::FileContent>,
+        _: &mut gpui::AppContext,
+    ) -> anyhow::Result<Self> {
+        sources.json_merge()
+    }
+}