extension: Add ExtensionEvents for listening to extension-related events (#26562)

This PR adds a new `ExtensionEvents` event bus that can be used to
listen for extension-related events throughout the app.

Today you need to have a handle to the `ExtensionStore` (which entails
depending on `extension_host`) in order to listen for extension events.

With this change subscribers only need to depend on `extension`, which
has a leaner dependency graph.

Release Notes:

- N/A

crates/extensions_ui/Cargo.toml

@@ -17,6 +17,7 @@ client.workspace = true
 collections.workspace = true
 db.workspace = true
 editor.workspace = true
+extension.workspace = true
 extension_host.workspace = true
 feature_flags.workspace = true
 fs.workspace = true

crates/extensions_ui/src/extensions_ui.rs

@@ -9,6 +9,7 @@ use std::{ops::Range, sync::Arc};
 use client::{ExtensionMetadata, ExtensionProvides};
 use collections::{BTreeMap, BTreeSet};
 use editor::{Editor, EditorElement, EditorStyle};
+use extension::ExtensionEvents;
 use extension_host::{ExtensionManifest, ExtensionOperation, ExtensionStore};
 use feature_flags::FeatureFlagAppExt as _;
 use fuzzy::{match_strings, StringMatchCandidate};
@@ -212,7 +213,7 @@ pub struct ExtensionsPage {
     query_editor: Entity<Editor>,
     query_contains_error: bool,
     provides_filter: Option<ExtensionProvides>,
-    _subscriptions: [gpui::Subscription; 2],
+    _subscriptions: Vec<gpui::Subscription>,
     extension_fetch_task: Option<Task<()>>,
     upsells: BTreeSet<Feature>,
 }
@@ -226,15 +227,12 @@ impl ExtensionsPage {
         cx.new(|cx| {
             let store = ExtensionStore::global(cx);
             let workspace_handle = workspace.weak_handle();
-            let subscriptions = [
+            let subscriptions = vec![
                 cx.observe(&store, |_: &mut Self, _, cx| cx.notify()),
                 cx.subscribe_in(
                     &store,
                     window,
                     move |this, _, event, window, cx| match event {
-                        extension_host::Event::ExtensionsUpdated => {
-                            this.fetch_extensions_debounced(cx)
-                        }
                         extension_host::Event::ExtensionInstalled(extension_id) => this
                             .on_extension_installed(
                                 workspace_handle.clone(),
@@ -245,6 +243,15 @@ impl ExtensionsPage {
                         _ => {}
                     },
                 ),
+                cx.subscribe_in(
+                    &ExtensionEvents::global(cx),
+                    window,
+                    move |this, _, event, _window, cx| match event {
+                        extension::Event::ExtensionsUpdated => {
+                            this.fetch_extensions_debounced(cx);
+                        }
+                    },
+                ),
             ];
 
             let query_editor = cx.new(|cx| {