Scope slash commands, context servers, and tools to individual Assistant Panel instances (#20372)

This PR reworks how the Assistant Panel references slash commands,
context servers, and tools.

Previously we were always reading them from the global registries, but
now we store individual collections on each Assistant Panel instance so
that there can be different ones registered for each project.

Release Notes:

- N/A

---------

Co-authored-by: Max <max@zed.dev>
Co-authored-by: Antonio <antonio@zed.dev>
Co-authored-by: Joseph <joseph@zed.dev>
Co-authored-by: Max Brunsfeld <maxbrunsfeld@gmail.com>

crates/assistant/src/slash_command_picker.rs

@@ -1,16 +1,15 @@
 use std::sync::Arc;
 
-use assistant_slash_command::SlashCommandRegistry;
-
 use gpui::{AnyElement, DismissEvent, SharedString, Task, WeakView};
 use picker::{Picker, PickerDelegate, PickerEditorPosition};
 use ui::{prelude::*, ListItem, ListItemSpacing, PopoverMenu, PopoverTrigger};
 
 use crate::assistant_panel::ContextEditor;
+use crate::SlashCommandWorkingSet;
 
 #[derive(IntoElement)]
 pub(super) struct SlashCommandSelector<T: PopoverTrigger> {
-    registry: Arc<SlashCommandRegistry>,
+    working_set: Arc<SlashCommandWorkingSet>,
     active_context_editor: WeakView<ContextEditor>,
     trigger: T,
 }
@@ -51,12 +50,12 @@ pub(crate) struct SlashCommandDelegate {
 
 impl<T: PopoverTrigger> SlashCommandSelector<T> {
     pub(crate) fn new(
-        registry: Arc<SlashCommandRegistry>,
+        working_set: Arc<SlashCommandWorkingSet>,
         active_context_editor: WeakView<ContextEditor>,
         trigger: T,
     ) -> Self {
         SlashCommandSelector {
-            registry,
+            working_set,
             active_context_editor,
             trigger,
         }
@@ -231,11 +230,11 @@ impl PickerDelegate for SlashCommandDelegate {
 impl<T: PopoverTrigger> RenderOnce for SlashCommandSelector<T> {
     fn render(self, cx: &mut WindowContext) -> impl IntoElement {
         let all_models = self
-            .registry
-            .featured_command_names()
+            .working_set
+            .featured_command_names(cx)
             .into_iter()
             .filter_map(|command_name| {
-                let command = self.registry.command(&command_name)?;
+                let command = self.working_set.command(&command_name, cx)?;
                 let menu_text = SharedString::from(Arc::from(command.menu_text()));
                 let label = command.label(cx);
                 let args = label.filter_range.end.ne(&label.text.len()).then(|| {