assistant2: Add support for using tools (#21190)

This PR adds rudimentary support for using tools to `assistant2`. There
are currently no visual affordances for tool use.

This is gated behind the `assistant-tool-use` feature flag.

<img width="1079" alt="Screenshot 2024-11-25 at 7 21 31 PM"
src="https://github.com/user-attachments/assets/64d6ca29-c592-4474-8e9d-c344f855bc63">

Release Notes:

- N/A

crates/assistant/src/context.rs

@@ -15,7 +15,7 @@ use assistant_tool::ToolWorkingSet;
 use client::{self, proto, telemetry::Telemetry};
 use clock::ReplicaId;
 use collections::{HashMap, HashSet};
-use feature_flags::{FeatureFlag, FeatureFlagAppExt};
+use feature_flags::{FeatureFlagAppExt, ToolUseFeatureFlag};
 use fs::{Fs, RemoveOptions};
 use futures::{future::Shared, FutureExt, StreamExt};
 use gpui::{
@@ -3201,16 +3201,6 @@ pub enum PendingSlashCommandStatus {
     Error(String),
 }
 
-pub(crate) struct ToolUseFeatureFlag;
-
-impl FeatureFlag for ToolUseFeatureFlag {
-    const NAME: &'static str = "assistant-tool-use";
-
-    fn enabled_for_staff() -> bool {
-        false
-    }
-}
-
 #[derive(Debug, Clone)]
 pub struct PendingToolUse {
     pub id: Arc<str>,