Implement vertical scrolling for extended keymap load error information (#42542)

This PR fix an issue where, if an error occurs while loading the keymap
file during application startup, an excessively long error message would
be truncated and not fully displayed.

Before:

<img width="1567" height="1056" alt="before"
src="https://github.com/user-attachments/assets/ab80c204-b642-4e8f-aaf5-eae070ab01a2"
/>


After:

<img width="1567" height="1056" alt="image"
src="https://github.com/user-attachments/assets/1b2ff2ce-3796-41d5-b145-dc7d69f04f11"
/>


Release Notes:

- N/A

crates/workspace/src/notifications.rs

@@ -593,9 +593,9 @@ pub mod simple_message_notification {
 
     use gpui::{
         AnyElement, DismissEvent, EventEmitter, FocusHandle, Focusable, ParentElement, Render,
-        SharedString, Styled,
+        ScrollHandle, SharedString, Styled,
     };
-    use ui::prelude::*;
+    use ui::{WithScrollbar, prelude::*};
 
     use crate::notifications::NotificationFrame;
 
@@ -617,6 +617,7 @@ pub mod simple_message_notification {
         show_close_button: bool,
         show_suppress_button: bool,
         title: Option<SharedString>,
+        scroll_handle: ScrollHandle,
     }
 
     impl Focusable for MessageNotification {
@@ -661,6 +662,7 @@ pub mod simple_message_notification {
                 show_suppress_button: true,
                 title: None,
                 focus_handle: cx.focus_handle(),
+                scroll_handle: ScrollHandle::new(),
             }
         }
 
@@ -777,7 +779,18 @@ pub mod simple_message_notification {
         fn render(&mut self, window: &mut Window, cx: &mut Context<Self>) -> impl IntoElement {
             NotificationFrame::new()
                 .with_title(self.title.clone())
-                .with_content((self.build_content)(window, cx))
+                .with_content(
+                    div()
+                        .child(
+                            div()
+                                .id("message-notification-content")
+                                .max_h(vh(0.6, window))
+                                .overflow_y_scroll()
+                                .track_scroll(&self.scroll_handle.clone())
+                                .child((self.build_content)(window, cx)),
+                        )
+                        .vertical_scrollbar_for(self.scroll_handle.clone(), window, cx),
+                )
                 .show_close_button(self.show_close_button)
                 .show_suppress_button(self.show_suppress_button)
                 .on_close(cx.listener(|_, suppress, _, cx| {