Refactor workspace notifications to use explicit NotificationId type (#10342)

This PR reworks the way workspace notifications are identified to use a
new `NotificationId` type.

A `NotificationId` is bound to a given type that is used as a unique
identifier. Generally this will be a unit struct that can be used to
uniquely identify this notification.

A `NotificationId` can also accept an optional `ElementId` in order to
distinguish between different notifications of the same type.

This system avoids the issue we had previously of selecting `usize` IDs
somewhat arbitrarily and running the risk of having two independent
notifications collide (and thus interfere with each other).

This also fixes a bug where multiple suggestion notifications for the
same extension could be live at once

Fixes https://github.com/zed-industries/zed/issues/10320.

Release Notes:

- Fixed a bug where multiple extension suggestions for the same
extension could be shown at once
([#10320](https://github.com/zed-industries/zed/issues/10320)).

---------

Co-authored-by: Max <max@zed.dev>

crates/assistant/src/assistant_panel.rs

@@ -46,6 +46,7 @@ use ui::{
 };
 use util::{paths::CONVERSATIONS_DIR, post_inc, ResultExt, TryFutureExt};
 use uuid::Uuid;
+use workspace::notifications::NotificationId;
 use workspace::{
     dock::{DockPosition, Panel, PanelEvent},
     searchable::Direction,
@@ -418,10 +419,14 @@ impl AssistantPanel {
                                 if pending_assist.inline_assistant.is_none() {
                                     if let Some(workspace) = this.workspace.upgrade() {
                                         workspace.update(cx, |workspace, cx| {
-                                            workspace.show_toast(
-                                                Toast::new(inline_assist_id, error),
-                                                cx,
-                                            );
+                                            struct InlineAssistantError;
+
+                                            let id =
+                                                NotificationId::identified::<InlineAssistantError>(
+                                                    inline_assist_id,
+                                                );
+
+                                            workspace.show_toast(Toast::new(id, error), cx);
                                         })
                                     }