assistant2: Add tool selector (#26480)

This PR adds a tool selector to Assistant 2 to facilitate customizing
the tools that the model sees:

<img width="1297" alt="Screenshot 2025-03-11 at 4 25 31 PM"
src="https://github.com/user-attachments/assets/7a656343-83bc-4546-9430-6a5f7ff1fd08"
/>

Release Notes:

- N/A

crates/assistant2/src/tool_selector.rs

@@ -0,0 +1,70 @@
+use std::sync::Arc;
+
+use assistant_tool::{ToolSource, ToolWorkingSet};
+use gpui::Entity;
+use ui::{prelude::*, ContextMenu, IconButtonShape, PopoverMenu, Tooltip};
+
+pub struct ToolSelector {
+    tools: Arc<ToolWorkingSet>,
+}
+
+impl ToolSelector {
+    pub fn new(tools: Arc<ToolWorkingSet>, _cx: &mut Context<Self>) -> Self {
+        Self { tools }
+    }
+
+    fn build_context_menu(
+        &self,
+        window: &mut Window,
+        cx: &mut Context<Self>,
+    ) -> Entity<ContextMenu> {
+        ContextMenu::build(window, cx, |mut menu, _window, cx| {
+            let tools_by_source = self.tools.tools_by_source(cx);
+
+            for (source, tools) in tools_by_source {
+                menu = match source {
+                    ToolSource::Native => menu.header("Zed"),
+                    ToolSource::ContextServer { id } => menu.separator().header(id),
+                };
+
+                for tool in tools {
+                    let source = tool.source();
+                    let name = tool.name().into();
+                    let is_enabled = self.tools.is_enabled(&source, &name);
+
+                    menu =
+                        menu.toggleable_entry(tool.name(), is_enabled, IconPosition::End, None, {
+                            let tools = self.tools.clone();
+                            move |_window, _cx| {
+                                if is_enabled {
+                                    tools.disable(source.clone(), &[name.clone()]);
+                                } else {
+                                    tools.enable(source.clone(), &[name.clone()]);
+                                }
+                            }
+                        });
+                }
+            }
+
+            menu
+        })
+    }
+}
+
+impl Render for ToolSelector {
+    fn render(&mut self, _window: &mut Window, cx: &mut Context<'_, Self>) -> impl IntoElement {
+        let this = cx.entity().clone();
+        PopoverMenu::new("tool-selector")
+            .menu(move |window, cx| {
+                Some(this.update(cx, |this, cx| this.build_context_menu(window, cx)))
+            })
+            .trigger_with_tooltip(
+                IconButton::new("tool-selector-button", IconName::SettingsAlt)
+                    .shape(IconButtonShape::Square)
+                    .icon_size(IconSize::Small)
+                    .icon_color(Color::Muted),
+                Tooltip::text("Customize Tools"),
+            )
+            .anchor(gpui::Corner::BottomLeft)
+    }
+}