extensions_ui: Add general structure for filtering extensions by what they provide (#24325)

This PR adds the general structure for filtering the extensions list by
what the extensions provide.

Currently flagged for Zed staff until we get some design direction on
how best to present the filter.

Release Notes:

- N/A

crates/extensions_ui/src/extensions_ui.rs

@@ -10,6 +10,7 @@ use client::{ExtensionMetadata, ExtensionProvides};
 use collections::{BTreeMap, BTreeSet};
 use editor::{Editor, EditorElement, EditorStyle};
 use extension_host::{ExtensionManifest, ExtensionOperation, ExtensionStore};
+use feature_flags::FeatureFlagAppExt as _;
 use fuzzy::{match_strings, StringMatchCandidate};
 use gpui::{
     actions, uniform_list, Action, App, ClipboardItem, Context, Entity, EventEmitter, Flatten,
@@ -210,6 +211,7 @@ pub struct ExtensionsPage {
     filtered_remote_extension_indices: Vec<usize>,
     query_editor: Entity<Editor>,
     query_contains_error: bool,
+    provides_filter: Option<ExtensionProvides>,
     _subscriptions: [gpui::Subscription; 2],
     extension_fetch_task: Option<Task<()>>,
     upsells: BTreeSet<Feature>,
@@ -261,12 +263,13 @@ impl ExtensionsPage {
                 filtered_remote_extension_indices: Vec::new(),
                 remote_extension_entries: Vec::new(),
                 query_contains_error: false,
+                provides_filter: None,
                 extension_fetch_task: None,
                 _subscriptions: subscriptions,
                 query_editor,
                 upsells: BTreeSet::default(),
             };
-            this.fetch_extensions(None, cx);
+            this.fetch_extensions(None, None, cx);
             this
         })
     }
@@ -363,7 +366,12 @@ impl ExtensionsPage {
         cx.notify();
     }
 
-    fn fetch_extensions(&mut self, search: Option<String>, cx: &mut Context<Self>) {
+    fn fetch_extensions(
+        &mut self,
+        search: Option<String>,
+        provides_filter: Option<BTreeSet<ExtensionProvides>>,
+        cx: &mut Context<Self>,
+    ) {
         self.is_fetching_extensions = true;
         cx.notify();
 
@@ -374,7 +382,7 @@ impl ExtensionsPage {
         });
 
         let remote_extensions = extension_store.update(cx, |store, cx| {
-            store.fetch_extensions(search.as_deref(), cx)
+            store.fetch_extensions(search.as_deref(), provides_filter.as_ref(), cx)
         });
 
         cx.spawn(move |this, mut cx| async move {
@@ -953,11 +961,15 @@ impl ExtensionsPage {
     ) {
         if let editor::EditorEvent::Edited { .. } = event {
             self.query_contains_error = false;
-            self.fetch_extensions_debounced(cx);
-            self.refresh_feature_upsells(cx);
+            self.refresh_search(cx);
         }
     }
 
+    fn refresh_search(&mut self, cx: &mut Context<Self>) {
+        self.fetch_extensions_debounced(cx);
+        self.refresh_feature_upsells(cx);
+    }
+
     fn fetch_extensions_debounced(&mut self, cx: &mut Context<ExtensionsPage>) {
         self.extension_fetch_task = Some(cx.spawn(|this, mut cx| async move {
             let search = this
@@ -978,7 +990,7 @@ impl ExtensionsPage {
             };
 
             this.update(&mut cx, |this, cx| {
-                this.fetch_extensions(search, cx);
+                this.fetch_extensions(search, Some(BTreeSet::from_iter(this.provides_filter)), cx);
             })
             .ok();
         }));
@@ -1162,7 +1174,41 @@ impl Render for ExtensionsPage {
                             .w_full()
                             .gap_2()
                             .justify_between()
-                            .child(h_flex().child(self.render_search(cx)))
+                            .child(
+                                h_flex()
+                                    .gap_2()
+                                    .child(self.render_search(cx))
+                                    .map(|parent| {
+                                        // Note: Staff-only until this gets design input.
+                                        if !cx.is_staff() {
+                                            return parent;
+                                        }
+
+                                        parent.child(CheckboxWithLabel::new(
+                                            "icon-themes-filter",
+                                            Label::new("Icon themes"),
+                                            match self.provides_filter {
+                                                Some(ExtensionProvides::IconThemes) => {
+                                                    ToggleState::Selected
+                                                }
+                                                _ => ToggleState::Unselected,
+                                            },
+                                            cx.listener(|this, checked, _window, cx| {
+                                                match checked {
+                                                    ToggleState::Unselected
+                                                    | ToggleState::Indeterminate => {
+                                                        this.provides_filter = None
+                                                    }
+                                                    ToggleState::Selected => {
+                                                        this.provides_filter =
+                                                            Some(ExtensionProvides::IconThemes)
+                                                    }
+                                                };
+                                                this.refresh_search(cx);
+                                            }),
+                                        ))
+                                    }),
+                            )
                             .child(
                                 h_flex()
                                     .child(